Many of us are familiar with this common piece of wisdom:
Beer then grass, you're on your ass.
Grass then beer, you're in the clear.
It's pretty hard to forget this rhyme. But the problem is that, after five or six beers, everything seems like a good idea. Including, but not limited to, a few cones.
So, after a few beers, many of us choose to ignore this, and many other, pieces of common sense. They generally only ever do it once, though.
ALWAYS OBEY THIS RULE. FAILURE TO COMPLY WILL RESULT IN BARFING.