Why do Serbians guys have a bad reputation?

So I've been seeing this Serbian guy lately and when I tell my friends he's Serbian they kind of go hesitant and tell me to be careful when it comes to them. I do take my friend's opinions into consideration but I'm just curious as to why they have a bad reputation. Apparently they are really smooth and charming and often have a lot of girls.

Have any of you guys heard this about Serbian men?

Also, I know I shouldn't stereotype all Serbian guys but I've told a few people and they all have the same reaction.
Why do Serbians guys have a bad reputation?
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