Is it ok for a 15 year old nephew to tickle his auntie's feet in a slow and smooth way?

Last night I visited my girlfriends house and her nephew was staying the night as well. I was cuddling her on the sofa (she was sat between me and her nephew) and all of a sudden her nephew started tickling my girlfriends feet.

This was not done in a funny 'haha' way to make her laugh - but it was done slowly and smoothly (almost seductively). Her response to him was that it was 'nice' and to keep doing it. I felt extremely uncomfortable and got up to get a drink. This tickling had probably only gone on for about 10 seconds until I got up, to which it then stopped.

My girlfriend and her nephew are very close and are always messing about with each other (as far as name calling, play punching, etc). I've not got any nieces or nephews so I'm not sure if this is normal or not?? I have no problem with the joking side of things, but this felt very strange!!

Her nephew had told me that every night that week (because he'd been staying over) that her feet had been sprawled over him. I wonder now if this is normal and if they were doing it every night.

I'm not suggesting for a second that there is anything untoward going on, it's just the situation itself seems strange and made me feel uncomfortable. I could never imagine myself feeling comfortable if someone tickled my feet in such a way in front of my girlfriend.

My girlfriend and I went to bed soon after, to which she asked me what was wrong. I didn't make a huge deal out of it, I simply said that I felt 'uncomfortable' which is why she noticed me squirming, sitting awkwardly, etc. She then went mad at me for saying that I felt uncomfortable and went to bed without saying a further word.

I have told her since that the situation made me feel uncomfortable and that she should respect how I felt. During the argument, I did suggest that the situation was 'sick' - was this wrong??

I keep imagining that if the roles were reversed and it was a 15 year old girl tickling her uncle's feet then it would possibly be a po