I've heard worse coming from my younger sister's lips and she's only 7. xD
Hmm... it depends, really. What kind of voice was the person saying the sentence in? If the voice tone was noticeably light-hearted, joking and warm - then it might've been just for laughs.
If the tone was deathly-serious, humourless and straightforward - then the person might have some serious anger issues. または あなた might've done something that really riled them up.
There are many things to consider....
How close the person is to you, whether they've 発言しました similar things to あなた before, whether they actually ever did any of those 前 things, what their history of violence/crimes/behaviours is...
あなた can confide in someone close to あなた and then see what アドバイス they can offer.
