To laugh AT someone as a pose to laughing WITH them.
Limes: "Hey that sounds very satisfying! Er......care to come round here after your sandwich Sarah so you get a double dose of satisfaction?"
Stu: "LOLATT *sniggers*"
To laugh at or with someone but at something more funnier than a "lol"
I just fell in dog poo !
Oh that's brilliant! Lolatt!!!