A fork of Rural Dictionary
Someone who is a 'dry arse' or 'dry' is someone who backs out of drinking alcohol for a reason which is not legitimate.
Person X: I'm goin to get so pissed tonight. Are you? Person Y: No, i'm gonna stick to lemonade, I don't want to get drunk. Person X: You fucking dry arse! Here, person Y is being a dry arse because he/she is backing out of drinking alcohol.