Funny Situations: A great way to create humor is to put ordinary people into ridiculous situations and have them try to act normal. In the movie, When Harry Met Sally, Sally makes a point about women faking orgasms while in a restaurant. The funniest moment is when the woman next to her says, "I'll have what she's having." It all seems so normal.
Funny Characters: Sometimes I'll have a character who is just plain quirky. Not the main character but someone who provides a bit of comic relief. You never know what they are going to do or say, and it keeps the main characters on their toes. In my novel, Getting Back to Delaney, I have three such characters...the three nosey grandmothers living next door to Delaney. Their antics are not without purpose, though. No matter how ridiculous they seem, their intention is to get the two main characters, Tyler and Delaney, together.
What scene from a movie or book struck your funny bone just right?