As a spoiled member of the upper classes I would have servants to attend my every need. A serving wench delivers my drink and spills it on me, of course this kind of insult cannot be tolerated and the wench must be made to pay for her clumsiness
An alternate and more fun scenario would involve two wenches. The first bringing the drink and spilling it, the second wench is the one who bumped into her and would also be responsible for the spill. In this case they would both be held responsible and have to make up for their carelessness.