I personally do not agree with fighting dirty. The brass knuckles should only be used if he uses something too. Besides when you go into a fight you have to ask youself some questions.

1 - Can I take this peoson or at least give him/her some damage and not get badly beaten in the process?

2 - Does this person have someone who might jump in?

3 - Do I have someone who could help me if I really need it?

4 - Is this person crazy and will he/she try to pull a knife?

5 - How bad can this backfire on me?

6 - If I do need to run, can I outrun this person?

Don't do something stupid. But if you can take him, then kick some ass Lol.