To see men in your dream represent an authoritative figure or a father figure. If you are a woman and dream that you are in a room full of men, then it highlights the masculine aspect of yourself. The dream forces you to acknowledge your authoritative and aggressive side. Consider also how the men are dressed as this will provide a clue as to what area in your life you need to assert more power. 

If you are a man and dream that there are only men at a party suggests that you are questioning your abilities. You fear that you are being overlooked or not measuring up to others. Or perhaps you are also expressing desires of blending in and not standing out.