Ice Cream Scream

Alright listen up, buttercup. This "joke" is a play on words. The person says they sat down to eat ice cream, and the next moment they "ice creamed." Get it? Instead of saying "I screamed" which is what you'd expect, they made it sound like "ice creamed" because they were literally about to eat ice cream. It's punny because it uses the similar sound of "ice cream" and "I scream" for a silly effect. Your brain is probably still processing that.