No one can argue the fact that Chris Pratt killed it in his role as Star-Lord in the various movies of the MCU. Unlike Pratt himself, Peter Quill didn't quite live up to the expectations. Throughout the two Guardians of the Galaxy films and the following Avengers movies, Star-Lord seemed to progress through the universe making mistake after mistake.
Overall he is still considered a hero. He stopped Ronan, foiled Ego's plans, and fought against Thanos with the rest of the Avengers. Unfortunately, all the good intentions in the world can't make up for all of the times Peter Quill seemed to just make things worse.
10 Stole The Orb
The entire first movie in the Guardians of the Galaxy franchise revolved around this orb and the Infinity Stone that was hidden inside. Originally the Ravagers that Peter Quill had grown up with were supposed to go and retrieve the orb, but in an act of rebellion, Star-Lord beat them to the punch and stole the orb for himself.
This set the events of the movie into motion, but the orb would have actually been safer in the hands of the Ravagers. Star-Lord only managed to play keep away from Ronan for a small portion of the movie before he got it anyways. His stealing of the orb only hastened the potential destruction of the Nova Corp.
9 Delayed For His Walkman
After a daring jailbreak that really should not have succeeded, all of the important characters were on board the Milano and ready to get away from the prison before any reinforcements could come and throw everyone back in their cells. Unfortunately for them, Peter insisted on returning to the prison for his missing walkman.
The walkman was absolutely important to him as one of the few gifts remaining from his deceased mother, but he risked the livelihoods of everyone on board that ship for a selfish reason. It was only chance that reinforcements didn't arrive and arrest all of them again.
8 Tried To Sell The Infinity Stone
Star-Lord and the rest of the Guardians decided to sell the orb to the Collector so that they could each get a ton of money and go their separate ways. The sale was going smoothly until the orb was opened and it was revealed that the Power Stone was hiding inside the whole time.
The Collector's assistant caused an explosion with the stone and the Guardians fled with the stone now back inside the orb. Instead of taking this powerful artifact to the Nova Corp, Star-Lord still decides that they should sell the stone for money. This inevitably leads to the stone being taken by Nebula and Ronan instead of being protected by a massive military.
7 Flirted With Ayesha
The second movie in the Guardians of the Galaxy franchise had the Guardians fighting some type of space beast as a job for the Sovereign. After completing the job and returning to collect their reward, Peter decided to start flirting with their leader, Ayesha, in front of the other Guardians and some of the Sovereign.
This isn't the worst thing he could do and it fits his character, but at the time he is getting feelings for Gamora and she's standing a foot away from him during this. His flirting also gave Rocket time to steal the batteries from the Sovereign and got Ayesha personally invested in bringing them back for Rocket's theft. Call it 30/70 for blame, but without the flirting, they would've left without giving Rocket time to steal the batteries.
6 Argued With Rocket
Tensions were understandably high as the Guardians fled in the Milano with the Sovereign fleet hot on their tails. Rocket didn't seem apologetic about stealing the batteries and Star-Lord was upset that the fleet was now shooting at his ship.
This leads to a massive argument as they run from the fleet as to who is the better pilot between Peter and Rocket. The fight combined with the chasing fleet and a nice field of asteroids led to the Milano being damaged and inevitably crashing. This one is again partially on Rocket, but Peter could have easily set aside his ego and anger long enough for them to get out of danger.
5 Ignored Gamora's Warnings
Peter's dad finally shows up, and it turns out that Ego is a literal planet. Peter begins exploring this other side of himself that he never knew existed, but Gamora wasn't too sure about his dad. She got weird vibes from him and didn't like how quick Peter was replacing his new family for a man he had just met.
Peter obviously ignores Gamora's warning and ends up alienating her in favor of his dad. This turned out to be the wrong choice as his dad only wanted to use him to spread his own influence throughout the universe. If Peter had listened to the girl he liked and had known for a while, none of the bad things in the latter half of the movie would have happened.
4 Fought Over The Plan With Iron Man
If there's one thing Star-Lord inherited from his father, it's his ego. It popped up briefly when he met Thor, but it came out full force once the Guardians team up with Iron Man, Spider-man, and Dr. Strange. As they tried to come up with a plan to face Thanos when he arrived, Star-Lord fought against Iron Man so that they would use his own plan.
The plan he came up with wasn't bad, but it could have been improved if he'd worked out the plan together with the other two thinkers of the group. Tony and Strange could have modified the plan enough that they may have stopped Thanos completely if it weren't for Star-Lord insisting on his own ideas.
3 Punched Thanos When The Heroes Could Have Won
This is the first thing that pops into fan's minds when asked how Star-Lord has messed up. Despite all odds, their plan went well and Thanos was fully subdued with the gauntlet ready to be taken off of his hand. Before they could finish the job, Peter decided to ask Thanos where Gamora was so he could go retrieve her.
Of course, Gamora was dead. She was sacrificed so that Thanos could get the soul stone and Mantis was able to relay that to Peter using Thanos' emotions. Peter ended up throwing caution to the wind and attacked Thanos in a petty display of revenge. All it resulted in was Thanos breaking free of the group and defeating them in the long run. Star-Lord played a major role in Thanos winning his first altercation with the Avengers and successfully wiping out half the life in the universe.
2 Came On Too Strong To Gamora
During the final battle in Avengers Endgame, Gamora from a different timeline rescues Quill from being killed when he loses a brief scuffle. He is obviously completely stunned to see her and approaches her completely forgetting that in his world she had died.
In his defense, he didn't know about the alternate timelines and couldn't have guessed that this was a Gamora who had never met him. However, he could have easily read her body language that showed she was uncomfortable and distant. Instead, he tried going in for a kiss and ended up driving her away even as she drove her knee into his crotch.
1 Creating Tension With Thor
There was a bit of tension between Peter and Thor when they initially met because Peter was intimidated and felt threatened. Now Thor plans on traveling with the Guardians and Quill still has the same old inferiority complex he suffered with before.
Their minor contest on who the actual leader was temporarily resolved with Thor agreeing that Quill is the leader of the group, but that isn't likely to last. The next Guardians of the Galaxy movie hasn't come out yet, but there's almost a guarantee that Quill's feelings of inferiority to Thor are going to cause some sort of mistake for the rest of the group.