Friends: The Worst Thing Each Friend Has Done!
6. Monica - Cut Chandler's Toe Off
Now, it's easy to look at this entry and say, "hey, that was an accident, so surely she deserves to be let off the hook for it", and you'd be somewhat right. This was not a deliberate attack, but while it is true that this was only a silly mistake (and partially the result of an awful insult the year prior), it doesn't change the fact that it's hard to do something worse than cutting off someone's toe.
This moment came in the brilliant flashback episode, "The One With All The Thanksgivings". After being called "fat" by Chandler the year prior, Monica decided to get revenge by seducing him and embarrassing him. But, after a clumsy mishap with a knife, she ended up severing his toe instead.
To make matters worse, the doctors revealed that it could have been reattached, but Monica unwittingly brought a carrot to the hospital instead of Chandler's little piggy.
Accidents can be forgiven, but very few people in the world - outside of cannibals and masochists - can say, "I've cut someone's toe off". Thankfully, their love was strong enough to pull them through. Still, Monica is a chef; she should be chopping vegetables, not pinky toes.