Is Mars in 12th house a very bad aspect, I read it in my astrology book?

I would consider your Mars to be on the ascendant...2� away is really close...so you have a Mars ascendant which means you could be a tremendous sportsperson...or a personal trainer, or pursue an army/navy career....you will be quite forceful and take initiative.....your Mars is in Cancer, which gives it a bit of softness, so your male ego can be easily wounded, and you can respond quite agressively....I would definitely consider martial arts for relaxing...Judo/Karate would be excellent....and in general, I would avoid really high risk sports like things with motorbikes or kitesurfing...be careful, be aware and don't take silly risks, use your Mars in a positive way and you will always be called upon as a leader.....Good luck!