Complimenting The Opposite Gender
You can freely compliment your mother, sister, wife, etc. so this is not an issue of the opposite gender. If you want to compliment someone else, you should be clear in your head about your relationship with them as well as your intentions. Please bear in mind that this is a very slippery slope and one thing leads to another quite quickly. I would advise anyone to remain very cautious in regards to any unnecessary interactions that may lead the other person to draw any unintended conclusions.