my gf is never, ever want to do it on her 1st n 2nd day of her period. but on the 3rd one, i think she is same like the majority. she's became more hornier than ever, LOL. but as a medical student, i suggest not to giving her oral (coz mouth is full of bacteria n sometimes, viruses. On the other hand, women at their period will be more susceptible to get infection because the blood vessel is rupture at that time.) and also remember to clean the penis also before penetration (coz sometimes, there's a lot of bacteria if the boys don't clean it). but for me, i don't think that it was grossed. hoho