Could be either or, but I find with people in the BDSM/kink scene it means they are ticklish, but don't like it and therefore you shouldn't tickle them. If someone says a statement like that it means you don't have their consent to tickle them and you shouldn't take it as a challenge. Although their tone of voice can play a big factor as well. If they sound the slightest bit annoyed or angered I wouldn't try it. If they say it in a teasing playful and you know them really well they could just be acting bratty and actually want you to tickle them.
It was in the mainstream context, not BDSM
Yup, ninefive isn't going to answer the question.
Why don't you just tickle her and find out for all of us? That way none of us have to be in the same uncertain situation and risk getting punched in the face.
Some guys out there are into having their balls kicked (I will find weblinks if you require). If you do it to me I will punch you in the face (well after I've finished vomiting on you).
Moral: We are into Ticking as lee's and ler's and find it highly erotic. Not everyone else feels the same way.
You also have the "damaged goods" effect. I realize it's a crass term, but it quickly communicates the idea. Some people growing up have bad memories of being tickled by siblings/creepy adult relatives and so they are hard-wired with negative connotations. Frankly, they are pretty much lost causes IF tickling is necessary for a relationship in your case. A slim chance might be erotic tickling, if they're willing. I knew someone online who was horrible ticklish on her feet, but became "engorged and tingling" when foot-worshipped.
As a psychologist told me once: behind each fear lies a desire..