Does anyone else find self-described nice people are often deep down the biggest d**ks?

In my experience people who describe themselves as 'nice' are usually the complete opposite deep down. For example my friends ex-girlfriend said she was 'a nice girl'. And even if you asked her a hypothetical question about something she'd say in a really childish put on voice 'that's mean I wouldn't do that'. Then she got a reputation in my group of friends for being 'really nice' even though she never did anything that made you go 'wow how nice of her', the whole reputation just came from her self-proclaimed niceness. I never actually fell for the act and a few weeks ago it turned out she'd been cheating on my friend. I have another friend as well who describes himself as 'different to other guys' and 'nice and honest'. Again he never actually does anything that makes you go 'wow what a nice person', it's just based on his self-description. And he gets away with lies and doing d**kish things because people are like 'no hes nice he wouldn't do that'. I know another friend on the flipside though who plays a lot of jokes and tells a lot of lies (not big lies just lies for comical purposes) and for that reason gets tarnished a d**k and no one (bar me) trusts his credibility even though hes actually a very nice guy when hes not joking around.