The problem with talking about tickling
Common blunder this: There's basically nothing you can do now except wish you had never said anything, pretend you didn't, learn your lesson, and hope it hasn't really "weirded her out".
I really can't see the point in talking seriously to a girl (one you enjoy tickling) about this kind of thing unless you are in a proper relationship and have got to the point where you feel she needs to know. Tickling is meant to be light hearted play, and if you blurt out "I'm into tickling" you can't expect her not to be thinking quite what you meant next time you tickle her. If you only want to play around, making said announcement only casts the whole hting in strange light, and hence ruins it completely. Even if I felt I could easily get away with a girl knowing, I would MUCH prefer to just let them figure it out by tickling them all the time and making my enjoyment obvious. (also more fun than a serious chat 😉) Four girls in my life so far have known I have a fetish for tickling. Only two of those ever asked me about it and I never spoke of it until they asked. They only knew because I had decided to let them know by making it so obvious. By the time they ask, I already know they know and don't care, so it's easy to discuss it. Like I say two of them seemed happy to just know and not quiz me on it. One of them was actually my gf of 20 months. She knew it drove me wild tickling her, it was no secret: When she wanted sex she'd actually do stuff like grab things off me and refuse to give them back or just put her feet on my lap 🙂 Likewise, I figured out exactly what her quirks were and indulged her as often as possible. I loved how well we knew each other without speaking of it. It was like this deep, unspoken understanding that needn't be discussed. I guess I'll never meet someone like that again. Anyway, this is drifting from the point really so I'll shut up now. Bottom line is, keep your mouth shut. Divulge this kind of thing on a need to know basis, and you can carry on tickling as much as you want.
Also, "Ex-girlfriend, current friend" sounds nasty. I'm guessing you still fancy her. If you do, GET AWAY. I can't stress enough how painfull, time-wasting, and generally soul destroying it is to cling onto someone who has gone off you....