Is it normal to rub one out with girlfriends moms underwear?

Women can be very intuitively perceptive, so maybe at some level your girlfriend does suspect some of what's going on in your head, but you need to be aware that you just might be projecting and seeing things that aren't there. I would suggest that you be extremely cautious about letting your girlfriend know how arousing you find her mother's old underwear. Relationships between mothers and daughters can have all sorts of weird undercurrents and unspoken tensions going back years, and any guy who dares to get involved in that is playing with fire. And, of course, there aren't many women who like the idea of their guy having sexual fantasies about another woman, no matter who she is.

As for why you find this arousing, who the fuck knows? It can be very difficult to pin down the source of fetishes, since they seem often to be rooted in events that happened in the first few years of life, and childhood amnesia makes memories of that period completely inaccessible to us as adults.

Many people find the thought of violating taboos highly arousing, and what you're doing is definitely contrary to several rules of what's socially acceptable, so perhaps that's the main reason your buttons are pushed so hard by what you're doing. You don't say anything about finding your girlfriend's mother attractive, so I assume it's not about that.

My view is that we all have the right to fantasise about whatever the hell we want. As long as we're able to keep those thoughts securely locked in our heads and we're able to compartmentalise fantasy and reality, I think it's a case of no harm, no foul. Fantasies and fetishes become a problem only when they - or guilt about thinking of such things - makes our real-world life difficult for us. They can become a serious issue when we allow ourselves to act out our fantasies in the real world and this has negative consequences for others.

So I think the question you should be asking yourself is if your fascination with your girlfriend's mother's underwear is having a negative impact on your relationship with your girlfriend or her mother. If it is, then you might have a real problem.

That's a harmless fetish

When you put a pair on your head, do you situate the but part over your nose?

Like you said, not like you can really smell anything but just knowing your nose is right where the mom's ass was, I guess that counts for something.

If they're not solely your ladies panties, your fucking up.