The only time I can honestly 100% turn off ticklishness is when I'm around my immediate family. Something about mixing the two just makes me wanna. I don't even have to try -- I'm just naturally not ticklish around them.
Under any other circumstances, I can block it out for a short time if I focus really hard, but it doesn't last.
Wow... same here.
As bad as I am, the weirdest thing happened when my kids tried. It just doesn't work for them. In fact, my kids are convinced that their mom isn't ticklish at all. If they only knew.
I have also noticed...
Sometimes if I'm in a pissy/sad/frustrated enough mood, or if I don't know (or care much for) the person that well who is doing the tickling, that little switch flips and I lose the ticklishness then too.
I guess what it boils down to is the better my mood and the better I know and like you the more ticklish I am.