One of my favorites that hasn't been mentioned is in
Goodbye Kitty
Reese finds Lois' diary, reads it, and he thinks it was written by a girl in school. On the last scene of that episode, Reese is reading the diary in his room. He is reading the part where the girl was about to kiss her boyfriend. So Reese imagines himself kissing the girl, and right before he is about to kiss this gorgeous beautiful girl, Lois comes in the room, and tells him "what are you doing reading my old diary" and he suddenly imagines Lois is about to kiss him instead of the girl.
Hard to explain on paper, let me show you:
Before he knows she is Lois:
After he knows she is Lois:
Remember now? lol it was a masterpiece ending. I always rewind it and watch it a couple of times.