Seen it so many times in my life. Guys intimidate other guys and when they don't respond they get braver thinking they are invincible. It confidence grows and grows with each new victim.
Had a relative like that. He would get in the face of anyone over just about nothing. His confidence was huge because no one ever physically fought him. One day in a pizza place the owner told him to chill out and behave. He of course challenges him to fight thinking he would back down. The guy broke his nose with one shot and then they grappled for a bit before it was broken up. He had his tale between his legs for quite awhile.