It is a rather stupid threat sometimes, and saying "kill" like that isn't unique nor does it match a character's personality all the time. It's best if it's in roleplay you say something that could match the character's personality for battles and threats, but not everyone's a professional in roleplay. Though, that's only my suggestion instead of threatening to kill.
Take Warrior Cats, for example. In another turn, they in fact do threaten to kill in the books in a different said way but they don't actually kill. Some times it's just threatening to "shred" you. Though, blurting out "kill" like that... does get rather old. >.>
In other words I have to agree, it is a bit overused. Utter anger may cause a character to say to another out of hatred, but just blurting it out like that isn't really the best thing for roleplay in my opinion... Now you pointed it out.