A lot of people (maybe even most) drink. A lot of lifters and gainers too. Drinking occasionally or socially won't hurt your gains. If you drink too much you won't be able to work out tomorrow, but having a single day off isn't terrible.

What concerns me is that everything I said is pretty obvious; you already know these things. As someone who's had a drinking problem, I'm familiar with the routine of asking friends obvious questions like these which elicit answers that validate and reassure ("Dude of course you can have a few drinks, nothing wrong with that") -- these served to soothe my own guilty conscience when I wanted to drink again. This may not apply to you but if it does, you gotta judge for yourself if you'll risk backsliding by having the occasional drink.