For people who do Jiu-jitsu. Do you like wearing a gi/think it's cool?

I don't know about cool, but it's functional in judo and bjj. It provides a very sturdy clothing that roughly mimics everyday clothes. Imagine training in normal long sleeve shirts in judo and bjj. You'll need to get a new shirt every other class.

Personally I would prefer if we updated the gi to a more modern cut clothes in shape of t-shirt and such, but it's not a necessity. Also I can understand the wants to hold on to the traditional roots.

a gi is not compulsory in any of the martial arts.

However, It is often used to provide a kind of uniform for various schools of m.a., and, when there are many students, it's useful to show off the colour of the belt (level of the student) achieved to date.

(me, I learned karate, judo and jiujitsu without the "pajamas" -- couldn't afford one and few of the others with me could either.)

I don't particularly enjoy it, but I recognize that learning clothing grips, and defending the same, helps one to become a better martial artist.

If wearing a Gi feels the same to you as wearing a superhero costume, then go for it!!!

Wearing pajamas? No, its bucking lame.