These days, I've been obsessed with Baidu Tieba and wow. Chinese people love "slang", but they're usually just puns or a change of pronunciation. I will keep adding to this list when I come across/remember new ones, so keep checking back!
My format for this list: "Slang"("pronunciation/pinyin") --> "Actual word (if any)": "definition". "variations"
General
有木有 (you mu you)--> 有没有 (you mei you): is there any
米 (mi)--> 没/没有 (mei/mei you): none
神马 (shen ma)--> 什么(shen me): what
肿么 (zhong me)--> 怎么 (zen me): how
妹纸 (mei zhi)--> 妹子 (mei zi): Little girl, used to sound cuter. The "zhi" can be replaced by mostly any word pronounced the same way. This is also used to replace many words with "zi"
锅 (guo)--> 哥 (ge): (Older) brother. 果(guo)
天朝 (tian chao): China
打酱油 (da jiang you): passing by
路过 (lu guo)/ 飘过 (piao guo): passing by
同志 (tong zhi): homosexual. Literally, comrade.
攻 (gong): the one in a gay couple who "gives". 小攻 (xiao gong)
受 (shou): the one who "receives" 小受 (xiao shou), 受受 (shou shou)
For fangirl/boy purposes
本命 (ben ming): My life, basically the one you love the most.
男神 (nan shen): God, your favorite male celeb.
女神 (nv/nu shen): Goddess