“Nothing is true” – This is actually part of the tagline of the video game Assassin’s Creed and made me laugh when I saw it for the first time and heard so many fans repeat it like it’s the greatest thing; it sure sounds deep. Too bad it’s self-defeating.
If nothing is true, the statement itself falls under that category, making itself false and thereby irrelevant. Congratulations!

“Everything is relative” – Really? For everyone? Everywhere? At any time? Sounds like a very absolute statement to me. This is my personal favorite and also self-defeating.

“We can’t know anything for sure” – Another good one and the sceptic’s best friend. Unfortunately, it’s self-defeating, too. It seems like we at least know for sure that we can’t know anything for sure.

I hope this small overview was helpful. Beware of those absolutes!