But now I read in the internet that polish guys don't like intruders from another countries thinking that they go there to steal their women, and they may start troubles in a bar or in a night club etc... just for no reason, is that true? do i have to have friends over there to be there with no troubles?
Not true at all. You'll have a fantastic time. Just don't look for trouble when you leave the pub/club.
There are plenty of places to meet people when you're out. Nowhere specific.