The Urinal Wars

I just had a neat thought. what if earth went to war with an alien race because they looked like urinals? you know, they show up, all diplomatic then, while the leader is meeting with the president - some tourist pisses on an elite guard.
"... that's right, Jim, and if you can see what is going on behind me - the aliens seem to be bombarding the planet with some type of small white disc. They have a clean, chemical smell to them, and they look like large asprins except- wait -something is happening..... PISS!!! THEY ARE URINATING ON EVERYTHING!!!!! RUN FOR YOUR LIVES!!!"