Then there's a bug making it inconsistent for me, because I can definitively tell you that clicking on someone sometimes doesn't use a turn.
Actually, the skills were bugged when I first started. I thought the baseline you could carry was 3 from the getgo, because unlocking an "Efficient Barmaid" level let me carry four drinks--the last one was floating on the other side.
I also seem to remember that getting groped multiple times at one table uses up multiple turns--if that's not intended, then that's another bug. If that's intended, then it doesn't seem to fit the "deterministic" mold.