As a movie nut, its hard to pare down to the "most" of anything in movies. The one moment in film that has never ceased to amuse me since I saw it was from Mystic Pizza.

I even forget which principals were involved, but after one of the male characters (Vincent DoNofrio I think)  thinks his girl (Lilly Taylor ?) has cheated on him, he proceeds to dump a truckload full of live shellfish into her convertible. Once he realizes he is mistaken he looks at her and says

"I fucked up."

to which she replies... "Yeah, but you gave it 100%"

That moment of acknowledgment and forgiveness has always made me smile.