Megan Fox Images

It is wrong to someone else to photos during sex? My GF is pissed ..? Thus it was during dinner a few nights ago with friends and l argument took on sex. I said essentially Yeah usually when they were having sex I'm imagining Megan Fox in the head (l hot actress from Transformers.) As I'm doing my GF, but in my imagination Im not thinking about her at all, Im pretending I'm doing and imagining Megan Fox Megan Fox naked and do bad things in my head. This is really wrong? Whats the big deal? its only in my head. My GF is super pissed off and not talk to me. I have to pretend to think about her during sex?