Licking a woman's shoulder, because she is a woman, is clearly a sexist act.
No; it's sexual harassment and assault, but it's not sexist. Sexism would be if someone said "you're female, therefore you want to have your shoulder licked".
It is sexist because the assumption made is "you're female, and thus I can lick your shoulder and you will not mind, and if you do mind it's your own fault for being a woman in this place with lonely men".
Unless you're seriously trying to tell me that there are men walking around defcon licking the shoulders of other men as a clumsy come on.
I don't think that assumption was being made. It seems more likely to me that the culprits don't care if the victim minds having her shoulder licked -- most likely, didn't even think about it.
No; it's sexual harassment and assault, but it's not sexist. Sexism would be if someone said "you're female, therefore you want to have your shoulder licked".