A Bruce, is a friend(s) that makes up excuses not to go have a boys night out.
You're out with your boys for a boys night out. One of your boys turns to you and says he has to leave. You turn to him and ask why. He then says he has to go chill with his girlfriend or just doesn't feel like having a late night out... If it's before 11 PM, he is being a BRUCE ! When he insists on leaving you simply say " Don't Be A Bruce "
A Bruce is defined by a male friend of yours that is giving up drinking with his guy friends to hang out with his friends because he feels "tired" or needs to "hang out with his girlfriend".. Or leaves a night of drinking early because of these reasons.
Out with a couple of friends one night, and one friend has to leave around 10 PM to go chill with his girlfriend on a boys night out! He would be labeled a BRUCE !