"It is what it is."
It is lazy, circular, a cop out and means next to nothing. Vague enough to pass as a wise quip, to some. It is not.
Also not so much a saying per sé, but people who use quotes of famous people at the bottom or ends of emails. As if that implies a personality. If you are going to use something you think sounds smart, at least try to come up with that something yourself.