There is a Veronica/Archie tickle scene--but, sadly, I cannot tell you which comic it is in. I remember reading it twenty years ago at my cousins' house in Long Island, and I never forgot it.
In the story, Veronica does a George Jefferson/Harry Bentley and walks barefoot on Archie's bare back to try to help him with a back problem. Her toes accidentally tickle the crap out of him, and he laughs so hard that she almost falls off.
featherfingers: There is also a scene where Miss Grundy (and Mr. Weatherbee and someone else--Miss Beazley, maybe?) gets tickled. I think it is in Faculty Funnies #2, but I could be wrong. Those three and Prof. Flutesnoot become super-heroes, and they battle a villain who has a tickle ray. It hits the other three but misses Flutesnoot, who saves them.
Three other scenes I remember...
Reggie's bare foot is used as a model in anatomy class while Archie uses a pointer to explain each part on its sole. Unfortunately, he accidently points or scrapes too much, and Reggie is reduced to giggles.
Alexandra (of Josie and the Pussycats) uses the magic powers she had for a few issues to cast a tickle spell on a nasty nightclub manager.
I know that Big Moose was tickled once, but I don't remember who did it. I don't think it was Midge.
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My vote: Sabrina and magic tickling, just like featherfingers.