It's kind of hard to read what was said.
But I guess he said,"Die".
/That's certainly rude but really not that bad here. He may have said it with love. That's why he should have included an emoticon to let you know if he was really serious or was just kidding.
//At least he didn't go on and offer you 100 draws.
I understand that chess is frustrating. Yes, I had MANY MANY frustrating losses where i played like, tbh, crap. And especially hurts when its a time win for the other guy. But still, when you blunder, its not fair to abuse the other guy isn't it? :/ When somebody has just a king but is trying to win on time, okay, that situation is understandable. But this?