Gf wants me to wear skinny jeans

I do not think this is a good idea for the sake of my manhood-in more ways than one :P
I'd usually be a 32 and go for boot-cut etc., but she keeps bringing this up!

Having said that isn't the fact she thinks they'd suit me a compliment?

honest answer is if you aren't comfortable trying on skinny jeans. Try slim fit jeans, they don't feel restricting at all and I bet they would suit you. and im not saying it to help you compromise with your girlfriend even though in my opinion there isn't anything wrong with taking advice from a girlfriend, doesn't make you less of a man to trying out new things to a good extent. Im saying it because I do think you will suit slim cut jeans, because the secret to good style is making sure things fit well and boot cut looks baggy.

Maybe not to you... But I've got these things called "leg muscles", most slim jeans look as though they've been painted on.

well jeans are meant to fit well around the thighs but yes I suppose if you are very well built and do lots of squats then the jeans feel like they are painted on. However I think most men who have averagely built legs can fit into slim cut jeans.

I mean do these really look that restricting on most men?
http://www.mrporter.com/product/301277

On the model, no, but then most men are not models. And I'd also suggest that most men do no have a spare £200 to be spending on jeans. I'd rarely spend a quarter of that.
Lots of brand fit differently, and of course individual preference comes into it, but all the 'slim cut' jeans I've had (nb, it is only jean, though, slim cut suit trousers have been absolutely fine) have felt incredibly restrictive and made sitting down uncomfortable.