I'll just start with the reality for me, the act of tickling gets me aroused. I don't know why, but it's just the way it is. If I'm with family or friends and tickling starts in any capacity, I leave because to get those aroused feelings with people like that is not a comfortable feeling. The irony is that I'm actually asexual in the sense that I have NO desire for sex. It doesn't excite or interest me in the slightest. Tickling does. This may be an odd way to put it, but tickling with a girlfriend is like my version of sex. It does it for me.