It's happened to me a few times.
Especially when I'm weak, and trying to get cards.
It just pisses the hell out of me, I've spent so much time getting the health down and someone just comes along and kills it in a few shots then asks me if I want to buy it off them with freaking coupons.
Oh my god. No I don't want to spend my money on something I've worked so hard to get and you to just take it away from me.
BAH DIE.