Why do people think tatoos look cool?

Honestly, no idea. I guess people think tattoos are cool and think they're different if they have tattoos. No offense, but in my opinion it's exactly the opposite.

Given the category in which you asked the question, I'll venture that people think tattoos look cool because it "jazzes them up".

 I don't especially on woman where I fend them a real turnoff. 

Some people do and some don't.  I don't see why you're posting this in jazz.

People have different likes and dislikes. Many people like tatoos and they get them for a variety of reasons. What does that have to do with Jazz?

Because it is art. Art is cool.

This is a short step from those people who wear T-shirts and hats that they feel have to broadcast their life philosophy, religion, lame humor, political position, etc.  NOBODY CARES or wants your opinion, until they actually ASK for it.  There are specific people or groups who might get a tat to commemorate a very special situation - death of a loved one, membership in the armed forces or significant fraternal group.  There are also many people who REGRET a tattoo - and then, will pay and suffer to have it taken off.  There are doctors and tattoo artists who will remove for FREE, tats from gangs. It is their body and their choice - just not mine. 

Some can be sentimental

Idk cause they do.