Originally Posted by
rbwpi
I don't see the need to have a long dissertation with the parent. I would just make it clear that if the problem persists, the fecal matter will hit the fan. Might suggest the possiblity of accidently spilling my drink on them and other possible mishaps of an accidental nature.
Dissertation?

It's 3 sentences, takes 10 seconds and both times it was very well received.
Your course of action is much more effective it sounds