There is nothing RUDE in this word. It is word used by young generation, and it is form of slang. This word belongs to the group of SOFT swears.
Zajebiste does not have a defined meaning in Polish languages because like I said it is form of slang. It can be used to express your feelings.
You can say:
You have wonderful voice. –> You have ZAJEBISTY voice.
It was a great show.–> Show was ZAJEBISTE.
REMEMBER, it is form of slang …. so it does not sounds good if an adult use it in the sentence.
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