"I don't see enough evidence to believe this" and "you are a liar" are two totally different statements.
Not really, if the OP says "craziest thing I have ever SEEN..."
OP say that they have witnessed this, it's either truth or a lie.
You say you "don't see enough evidence to believe this" indicates you believe the OP is lying.
Seems easy enough.
And as far as the jumper, well, I have felt that way about Delta a few times myself....