From 1963's Action Comics #306 (by Robert Bernstein and Al Plastino), Clark Kent and Lois Lane are at the Daily Planet's Christmas party when Perry White pushes Clark under the mistletoe and then compels Lois to go there, as well, so that she has to kiss Clark.

The rest, as they say, is comic book history...

Damn, Lois and Clark sure have a complicated relationship, don't they?