(Non-perverted) Tickle games?

I was just wondering if there are any kind of games you could play that involve tickling. I'm super ticklish and I love it when my two best friends just start tickling my feet, belly, belly on, underarms, and sides. I know that they like tickling and being tickled too. So I was wondering if there were any games that we could do at our next sleepover? And please don't suggest anything ual...That's gross.