Jelly and Jam

Do you know the difference in Jelly and Jam?..... well you can't jelly your dick up your girlfriends ass!

If you ever watched "How I Met Your Mother", this joke was referenced. The actress Alyson Hannigen (who played Lily) was pregnant and needed to take time off from the show. So in one episode they had Barney start to tell this joke and then they cut to after the punchline, with Lily saying "That's it! I need a break from you guys" and walking out the door.