Ik everyone collectively agrees that The Spot would be an evil ler (which I agree he would be), but considering his backstory about how his family "can't even look at him anymore," he's probably super lonely and touch starved. I can absolutely see him being an absolute mess of a lee. There's one scene where Miles leaves him tied up in a web for the cops. I could see Miles accidentally finding out The Spot is ticklish through one of those encounters.
EEK THIS!! in an alternate universe where the spot doesn't become a Thanos level threat to miles, and he just stays a goofy villain, this would 100000% be the case!!
Honestly I headcanon that if he was tickled, he'd accidentally make a portal and fall through it like he did when he first met Miles:
THANK YOU FOR THIS, ANON!! Best idea EVER