Q: Why do I always see gays in the roundabout?
A: They couldn’t go straight.
Alright, listen up, buttercup. The joke is that "straight" has two meanings. Being "straight" as in not gay, and going "straight" as in not turning in a roundabout. It's funny because... well, it's not that funny, and you probably don't get it because you think the earth is flat.