What is that mean in the following conversation (Inception movie):
Arthur: You couldn't have peed before you went under?
Yusuf: Sorry.
Eames: A bit too much free champagne before take off, Yusuf?
Yusuf: Ha ha, bloody ha.
It looks contradictory to me, because "bit" usually means a small amount of something, but "too much" has the opposite meaning. Could you explain that?