What does BT joke mean?

This is a disgusting joke! ————————— Hey hey! Recently, I wrote a BT joke for everyone to see. Absolutely original! !

My boy once chatted with a girl on the third day of this year. I asked her, "Why do you girls like squatting to pee so much?" Is it cool? "She said," girls can only squat to pee, ok? Then let me ask you: Why do boys pee standing up? You answer! ! "Ha ha, I thought she must let me answer:" Boys can only stand, ok? "However, she was so naive that she was all wet-I said to her confidently," You don't know this. Boys are all-around players, like to stand and squat, and do whatever they want ... "-She was very surprised, and her mouth opened wide-she said," It's amazing! Brother, can you also teach me to pee standing up? " I shouted, "Attention! Stop! Look at me! " She did, standing straight, staring at me with bright eyes, not daring to blink. I touched her head and said, "Hmm! Not bad! Very energetic! You are very self-motivated and worthy of praise! ！” She snickered happily, and then I said to her sadly, "You are very motivated in your studies, but with your qualifications, it is difficult to achieve great things." I can't teach you! " She said to me a little worried, "You must teach me, and in return, I will teach you to squat and pee! ""I said to her, "Didn't I tell you? I have long known that I have to pee squatting. At least when I am four years old, I don't have to take off my pants when I squat, just take out the meat stick .................................................................................................................................. Can I eat? " I said, "Er ... @ #! $ @ #% # $ $ ............ ",she said," Can I borrow it? " I'm speechless at once! Take it!