TY– Thank you, IDK– I don´t know, IKR– I know, right?
LOL– Laughing out loud,
OMG– is Oh my god, an expression of shock or surprise
WTF– Another vulgar but very common expression, standing for «What the f***.
SMH– Shaking my head, an expression of disapproval.
ATM– at the moment
BTW– By the way
FYI– For your information
ASAP– As soon as possible
AFAIK o AFAIR– as far as I know, or recall.
OTOH– on the other hand
TMI– too much information,
NSFW– not safe for work, used to warn people not to open an image or click on a link
IMO, IMHO– In my (humble) opinion
BRB– Be right back
IRL– in real life, as opposed to online
J/K– just kidding, meaning the person is not being serious
YMMV– your mileage may vary.
YOLO– or: you only live once