I think we're seeing a fair bit of overlap here but I would say that it's just something enjoyable, sexually or not. It's fun to laugh and play like that but it can be arousing if that's how the participants want it to be.
Honestly, any kind of brush could work depending how sensitive she is. Toothbrush, paintbrush, brushes of varying size and materials. Just get a bunch of different things at the dollar store and experiment to see what she reacts to.
Yeah, well it sucks knowing they're ticklish but just hate it and won't let you do it. My most recent partner was like that. I knew she wouldn't budge on it.
My first gf though, she hated having her feet tickled (she said it was like a legitimate form of torture), but she liked pleasing me and...