When someone trys to act hard, tough or chavish infront of people, and you reply sarcastically with 'sorry hard' to show that they're failing.
It's also used to show that they're not hard atall, when they're acting like gimps.
prick: yeah i had a threesome with some lesbians last night, cool init blad!
normal person: shit, sorry hard.
geek: i got 102% on my maths exam!
normal person: wow, sorry hard.
some guy: im staying up till 4am tonight, cus I'm a badman
normal person: oh shit, sorry hard