Can any medics throw some light on this?

I have been having this odd situation ever since I can remember.... basically sometimes (once in a blue moon), if there is a contact/friction between my fingers/nails (or even when eating with spoon/fork etc) and anything metallic, I would feel very irritated and clench my teeth quite hard. Any idea what this might be? As a result, sometimes I can't even use the usual steel spoons but have to use plastic ones.
My bro has another such prob, though it is more when there is friction against silk & such fabrics.

p.s: To the Mods: I couldn't find a suitable title for this thread, so please do change it to something more apt

ooh god I really hate polystyrene you know the packaging stuff in tv boxes and the like it makes me absolutely sick if I hear it being scratched can't bear the stuff.

You definately aint alone, I experience the same sort of thing sometimes but with clothing items- for example, when I was at school a lot of people used to chew the bottoms of the sleeves on their school jumpers, and it was horrific for me to see them doing it, my jaw would (and still does just thinking about it!) go really tight and my mouth waters, the thought of it just makes me feel really weird!!! I cant stand the thought of anyone chewing any sort of clothing material, I dont know why!!!