The two stars were present at a 2012 MTV Movie Awards pre-show party on Sunday (03Jun12) to unveil the film's trailer.
In the movie, Lerman's character Charlie develops a crush on new friend Sam, played by Watson, and the couple end up in a passionate clinch - and Lerman is adamant he was delighted with the smooch.
He tells MTV.com, "It happened in front of a crew, and people were there, and we did it a few times. And that was it. It's kind of odd when you're doing it for a movie. It's kind of weird. She's cool. It wasn't as awkward as it could have been. It's Emma Watson, so I'm a lucky guy."