Essentially, when you give off the right angry vibe, people won't fuck with you. I don't recommend being angry around people you deal with every day - they'll think you're crazy and it can make holding down a job difficult.
But practice your angry vibe and you can radiate "don't fuck with me" without actually doing anything overtly angry. People won't be able to put their finger on exactly what they're being cautious about, but they'll have a strong sense that their life will be less troublesome if they leave you the fuck alone.
It's amazing how much you can actually freak people out by being emotionless - I've used what I call me "ice man" expression to sterling effect more than once. One of my favourite examples was way back when I was at college. I was with a friend at a "non-college" pub which could occasionally be a dicey proposition in a country town. I made my life more difficult by letting a hairdresser friend do a wacky haircut on me that nobody local would dare get - I had a design that looked like crop circles cut into my hair.
So I was walking up to the bar and I passed a table of yobs who felt compelled to comment on my haircut. The most eloquent of this little brains trust shouted "Nice haircut, mate," as I passed. This was actually quite threatening as their were four of them and they were all bigger than me. I was going to ignore them and continue on without acknowledging them but then I thought "No, fuck these idiots."
I stopped, then slowly turned to face them. I stared at them for a second, expressionless, then said in a monotone: "Thanks (long pause) I'm glad you like it."
This table of cavemen were absolutely gobsmacked. I was actually terrified of them but had managed to convince them I was totally fucking insane. The look in their faces made it apparent that they believed I'd swap my intended order at the bar for a bucket of their blood without hesitation.
Then the poet laureate of the group broke their stunned silence by stammering "No... uh, no. I, uh, really meant it. I think it's... ummm, a good haircut."
At this point I realised my bluff had worked but still betrayed no emotion - simply rolled my eyes and muttered "Yeah, right."
They were real careful not to make eye contact with me for the rest of the time I was at the pub.