Well, I've got three (two involving the House Robots, one I saw live).
The first was in an old Robot Wars event called the "Southern Annihilator". The finals featured Razer vs. Onslaught. Razer was having trouble crushing Onslaught, but pushed him to Matilda, who flipped Onslaught. Razer then decided to DESTROY Matilda, crushing her utterly (and perhaps becoming the first 'bot to take on a House Robot and win). It was hilarious. Here's the vid:
In the second House Robots' Revenge, Gravity and Behemoth faced Cassius Chrome, Growler, and Mr. Psycho. Partway through the fight, Growler charged Gravity. "Gravity thinks he can take on our dog of war," said the announcer. One quick pop from Gravity's flipper later, and Growler's been upended. "Oh! And he can!" It was the way he said it that made it funny.
Finally, in a live event three years ago, middleweight Hazard clone (kind of) Papercut's blade was damaged. For some reason, his team decided to replace it with a wooden board. His next opponent was the mean VS Heavy Metal Noise. The announcer said that Papercut would be called "Splinter" in this fight. It proved true. There were splinters EVERYWHERE after that thrashing.