Yes it is worse, outright OOCly threatening to kill a player character because you don't like what they're doing is the epitome of dickishness.
No. Just think of it as fair warning. Far worse would be actually going through with it without telling the other player beforehand that they've hit your tolerance level.
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"[This is perfect. I have always fought with these kinds of cards. You say that I have lost the moment I was dealt? It's just the same as always!]"