What does it mean when an opponent says good luck?

it bothers me when someone says that.i feel like they are saying that they are really good and that it will be a challenge to beat them, so that i need luck to beat them because they think my skill wouldnt do. for example before a game starts in internet checkers, billiards. Just wondering is that what they mean? Is it cocky when an opponent says that? Would you get offended if an opponent in a game said that to you?