My vote goes to the Enterprise second season episode "A Night in Sickbay". After Captain Jonathan Archer's dog Porthos takes ill after inexplicably accompanying Archer on a delicate diplomatic mission, and offending the natives by urinating on their sacred trees, Archer delivers the following ultimatum:
"If anything happens to Porthos, I'LL be the one one watering their Alvera Trees!!"
Seriously, did Archer just threaten to piss on a planet as a means of retaliation? That's something not even Kirk ever thought of!
Speaking that line surely must have been an even greater embarrassment to Scott Backula than all those Quantum Lep episodes which required him to appear onscreen in drag.