[luckyeddie]

Simple answer - very bad.

Certain chemicals present in fibre-tip and ball-point ink are definitely not good for you.

Benzene and phenol can be absorbed subcutaneously (through the skin) - writing on the skin is almost as bad for you as putting the pen in your mouth (and that's either end - the plasticisers in the little bung at the back end can also be toxic).

Chew on a pencil instead. The paint is non-toxic, the wood will do you no harm (apart from the methanol which could cause blindness) and the carbon in the 'lead' (graphite) will do you the world of good.