Stay away from your girl friend as far as possible...
Only engage in conversations that can be answered with a yes ma'am or no ma'am
Avoid all eye contact - this can be seen as aggressive
If an argument is necessary make sure you engage her in her own place, so the stuff she breaks is hers.
Do not blame her mood on her period, this is patronising, even though both parties know it really is her period that is causing her mood.
Look at the floor when in her presence, looking up may make her think you are
a) looking at other women
b) looking at men
c) looking in general
Remember lads, women are dangerous, just keep your heads down and wait for them to be all pink and fluffy again.