Okay,..... this one sort of piques my interest (I love statistics) and this very question once led to a fun little game with an old girlfriend.
Now I've read hypothetical estimates that the foot & shoe fetish crowd clocks in at as much as ten percent of males,... if you count all shades of its incidence. And I naturally include tickling as a component of the foot fetish 'cause that's how mine works. Couldn't speculate about non foot-related tickling beyond what I've seen on the TMF.
At any rate, I agree that the number may be not so small, after all,..,.... and about 25 years ago, a lady friend "assisted" me with a little impromptu research. Here's what we did....
Kate was in the classically-cliched female custom of keeping in touch with her circle of girlfriends via the good ol' telephone. I'd say about eight or nine of them,.... including long distance. Nothing crazily excessive, mind you. On one occasion she was chatting with one of these pals,... an older woman if I recall,... one living with a somewhat younger man,.. and I craftily tickled Kate's foot while she was speaking into the phone. She quickly stifled a surprised burst of laughter,... shot me an exasperated glare,.... and then tried to cover it with a fake cough and apology to her friend.
In a minute or two, I tickled Kate's foot again. Same reaction,.. same stifled fake cough,... same flustered little apology. But with the third assault, Kate simply burst out laughing into the phone,... yanked her foot away and this time she simply said, "I'm sorry,.. I can't help it,......M. is tickling my foot."
Well that was all it took. Kate's friend proceeded to regale her with girl talk stories of her boyfriend's prodigious foot & foot tickling fetish. (Kate covered the phone with her hand and grinned at me,... "She says Tom is constantly tickling her feet!")
Naturally this caused me to view my little prank as an actual survey polling mechanism, thanks to the afore-mentioned phenomenon of girl talk. Kate was intrigued with the idea, herself, and she happily went along. Over the next few weeks with each of her routine chats with her friends, we pulled the same stunt; I'd tickle Kate's foot a couple of times and she'd cover somehow,.... then I'd get her good and she'd erupt, then confess. Among all the girlfriends "set up" and probed in this manner, there were an appreciable handful of knowing and colorful rejoinders. The girls cheerfully disclosed their own husbands' and boyfriends' foot and tickling exploits and I'm gonna say we came in at around 3-out-of-8 volunteering comparable or related information.
Now 37.5% is likely an anomaly,.... but conducting the survey was most enjoyable,... some of the tales pretty interesting, too.