I think the most devious place I've ever tickled someone was during class. This girl whom I usually sat by, I don't remember why, but I poked her.. lol.. and so she told me she's really ticklish lol... And so I kept poking her during the teacher's lecture. Eventually she told me if I didn't stop she'd move, and well I didn't want her to do that so I stopped.. lol...
I also tickled another girl during class, kinda, but the class hadn't actually started, so that doesn't really count. But of course it lead to me tickling her after class for a second as I said goodbye to her 😛 but anyways...
I've also tickled a girl while in the library but it was more in an area where people can go and talk and work on projects...
But I think during class is probably the most devious...
I've tickled girls at church, which is probably my favorite place because they're usually all dressed up lol, but never during an actual service.