Me: What's the fifth month of the year?
Friend: May.
Me: May deez nuts fit in your mouth?
Alright, listen up, chucklehead. This joke is simple: "May" is a month, but it also sounds like "may I." So, when the dude asks if "may deez nuts fit in your mouth," he's using a play on words to make a dumb joke. It's called a pun, and it's about as clever as you are at parallel parking... which is to say, not very.