WTHAYD?

it basically mean WHAT THE HELL ARE YOU DOING?

DAD: do you wanna have sex
MUM: sure babe
...
SON: WTHAYD?!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

SYL

It means see you later

5:00pm

Simon: today I have to go to a party
Eric: Why?
Simon: because it's a birthday party
Eric: ohh ok
Simon: ok bye
Eric: SYL