Crazy huge dude

Ok, my ex girlfriend is going out with this crazy-ingly huge muscled dude and he wants to kick my ass and I am puny and scared. So I need to know where and how I can get a knife that is small and how I can carry it around my body at all times as to use it in case of defense (and defense only!).

I'm seriously scared and hope you guys can tell me how I can do this?

I prefer the crowbar to the shank.
But you should use- the screwdriver, trust me, thrust that shit in his bulge and he'll be in too much pain to move let alone be able to lay a finger on you before you're able to stab him with it again, and this time in a more effective place since he'll be easier to hit in said places, a good second spot to hit would be from the following: the neck, the heart, the cranium, the eyes, and the abdomen.
Hope it helps.