"But now I have written unto you not to keep company, if any man that is called a brother be a fornicator, or covetous, or an idolator, or a railer, or a drunkard, or an extortioner; with such an one no not to eat."
(Holy Bible, 1 Corinthians 5:11, KJV)
Get rid of your scumbag "friends," distance yourself from negative "family" members, give your pessimistic roommate the boot. Though it may seem as if you are capable of just "ignoring" the negativity that surrounds you, having it not affect you at all, it is better to have no negative stimuli in your life, lest you be tempted to give into it.
Ever heard of the saying, "you are who you hang around?" Well, it's mostly true. Druggies hang with druggies, successful people hang with other successful people, negative people hang with negative people, positive people hang with positive people. If you claim to be a positive person, then why hang with a negative person? What do you have in common with him?
Saying that you are not affected, at all, by hanging around negative people, is liking saying that a person could tap on your shoulder for 24 hours, straight, and that you wouldn't retaliate; sure, it's possible, but I assume that, eventually you will give in. At first, the negative stimuli seems harmless, and you may overcome it for a short while, but it can eventually overcome you. You should avoid, at all costs, any and all negative stimuli, just in case you have any unknown weaknesses.
"Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? and what communion hath light with darkness?"
(Holy Bible, 2 Corinthians 6:14-17, KJV)
Positive people have nothing in common, with negative people. So why have fellowship with each other, in the first place?
— Nio Pomilia