Is "take care" always a friendly utterance or can it sometimes be considered threatening?

A little while ago someone wrote to me, in a not-too-friendly internet exchange, "take care, man". I interpreted that as a threat, but now I realize that Americans often use this expression "take care" in a very friendly, benevolent way when leaving each other. So my two related questions are:

1. Considering this widespread usage, is it still possible (in the US) to use that expression in a threatening way?
2. If you wanted to threaten someone (!) what would you say? I'm thinking of some scenario in a film where a character approached by some suspicious guy would want to say "be careful [ I'm armed]". Is "be careful" right? Is some other expression more adequate?

Solution 1:

"Take care" is almost always used in a friendly way, or when genuinely warning somebody to be careful. It could conceivably be used as a threat, but the tone of the speaker's voice (or the context of the situation) would have to be very clear for it to be interpreted this way; it's more likely that in such a situation where you wished to issue a thinly-veiled threat, you'd instead use a more sinister phrase like "watch your back", or "don't get hurt".

Solution 2:

There is a stereotypical threat you might see in a gangster movie where an obvious bad guy says to a small business owner, "Nice place ya got here. Be a real shame if anything were to happen to it. Real shame." This is supposed to be intepreted as a threat even though the literal (word by word) meaning is a compliment. Only in a construct like that could "take care" be a threat. In regular usage it doesn't even mean "be careful" or "protect yourself", it means "well I guess we are finished talking now."