Actually, I think it would be a good idea to go drinking with someone who uses this app. Since they'll invariably forget X number of drinks throughout the night, you can offer to settle up the next day. "See? I only had two beers."
If you and your friend don't have the kind of relationship in which either of you can trust each other or forgive a beer or two, then you don't have the kind of relationship in which you'll automatically trust each other to have pushed the buttons on an app correctly.