I've noticed the most common thing is that people faking laughter don't want to feel out of breath or tired at all. Despite that being how an actual ticklee would be.
So they weakly struggle and fake laugh, then stop for a few seconds to breathe, and then struggle and laugh again, then stop for a second to breathe, then struggle and laugh, and so on.
Real ticklish people don't take breaks in their ticklishness.