Taken from dreammoods.com:
To dream that you are in your underwear, signifies a situation that has created a loss of respect for you. Alternatively, it symbolizes some aspect of yourself that is private. If you feel ashamed of being seen in your underwear, then it indicates your hesitance in revealing your true feelings, attitudes, and other hidden habits/ideas. If you are not bothered by being in your underwear, then it suggests that you are ready to reveal or expose something that was previously hidden.
To dream that you are not wearing any underwear, signifies fear that your secrets will be revealed.
To dream that someone is in their underwear, signifies an embarrassing and inexplicable situation. Alternatively, the dream means that you are seeing this person for who he or she really is.
To see dirty or torn underwear, suggests that you are not comfortable in your own skin and have feelings of inadequacy. You are uncomfortable about your sexuality and are overly critical about yourself.
*Please see also Panties.
To dream that you are in a gymnasium, indicates that you need to apply what you learned and incorporate it into your daily life. Alternatively, the gym may be telling you that you need to get more exercise.
To dream of a confrontation, represents a conflict or a fear that you are facing in your waking life. The dream provides a "safe" venue for you to confront your enemy or attacker, who you are afraid of standing up to in your waking life. You need to use your dream to overcome your fears. Next time you have this dream, tell your enemy or attacker that you are not afraid of them!