请问英语的“我想去小便/大便”怎么说？

文雅一点是：Nature calls.

普通点是：I wanna pee/I wanna poop.

I want to take a piss.(小便)
I want to make a bowel movement.(大便)
大便还可以说:to take a shit; to defecate; to take feces.

上面是正式的
i wanna teetee
非正式的

I wanna use the bathroom.

Excuse me, I want to go to the bathroom.