[sammyg2]

A tip is a REWARD for GOOD service.
It is NOT manditory, it is not automatic, it must be EARNED.

If a server dumps crap on me or one of my guests, that is NOT good service even if she is nice about it (unless of course someone else bumped her or caused the accident).
Having a server being careful enough to NOT spill sauce on the guests would be considered minimal expectation.
I would most likely NOT have left a tip.

PS $173can for mexican food for four? That's about $140 US. For that kinda change I would expect near perfection.