I was discussing this subject with a female friend not too long ago. I think that while same sex tickling isn't neccessarially "gay", that society's perception of such dictates the issue.
I see it this way: Many girls are very affectionate toward their female friends, whether the girls are gay or straight. Girls can kiss each other, and be very touchy feely, even if both of the girls involved are straight. If two girls in a shopping mall kiss each other hello on the cheek, or even tickle each other, most people will probably just shrug their shoulders, and go "Okay, whatever". I have had straight female friends in my life, who were currently in relationships with guys, and who tickled their straight female girlfriends.
With guys, its different: If one was to walk through a shopping mall, and see two men who havent seen each other for a long time, and the guys gave each other, say, a greeting bear hug, people would probably not think it gay, but, if one saw two guys walking through a mall, tickling each other all over, the first thought, whether they were gay or not, would be "Okay, why are these two guys tickling each other, they must be gay".
I myself have no desire to tickle, or be tickled, by another guy, ever, but that's just me. Any guys who are into same sex tickling, more power to them.
So, to answer the question: While m/m tickling isn't necessarially "Gay", society's perception of such is just that it is less socially acceptable for two straight guys to tickle each other, than two straight females to tickle each other, and, that if the guys do tickle each other, they must be "gay". It doesnt mean that guys who tickle each other are neccessarially gay, but society's perceptions of men just sees m/m tickling by straight guys, as less acceptable then f/f tickling by straight girls.
Mitch: