it should be "just give it a shot". You would say this to someone when you're encouraging them to try something (for example, trying new food, trying to do so something they haven't done before). "i'm pissed off" is the slang way of saying "i'm mad" or "i'm angry" it is should never be used in a formal situation, and is a light form of cussing, or bad language.

just give it a shot > just give it a try > Kiss her ! You wont know till you give it a shot and find out if she allows you to do it. I'm pissed off.>> you are not happy about something. I am pissed off with the service given to me . They think I have no money .