It feels physically uncomfortable when my girlfriend touches my butt.
My girlfriend likes to grab my butt on occasion, and I do not mind this psychologically, but when she does grab it it feels so weird physically that I compulsively jerk away. I try to relax myself to let her grab it, but it's like trying not to laugh when you're being tickled. I can relax enough that she can feel the surface of my skin there, and even poke at it without reflexing away, but it still feels uncomfortable.
This is by no means important to our relationship. It's pretty much a joke for us, it's not really provocative in any way. But, it still gets me wondering: Is it normal that it feels so weird physically to have my girlfriend touch my butt?
Some details (not sure if relevant): We've been together almost two years. I'm a guy.