DuvanMuvan, if you say "I don't want to be a Jehovah's Witness anymore", you'll be asked to put this in writing, and when you do, it will be considered a letter of disassociation. So you'be DA'd, not DF'ed. But the result will still be the same: complete shunning.
So, you'd better not say this phrase unless, of course, you have decided to actually DA.
If you don't want to be DA'd or DF'd at that moment, you can simply not give an explanation at all. They can't physically force you, we're not in the Middle Ages. Play by your rules, not theirs. You can also give an inaccurate or incomplete reason, such as, "I'm depressed, I've been very busy", that sort of stuff. It may sound as a lie, but hey, the WTS is constantly lying on topics such as evolution and everything else. You can also deny meeting with 2 elders, while accepting meeting with one. Simple safety measures.