Psychos are Bandits that charge toward you and try to slash you with their weapon. Sometimes, they may sit back and throw the weapon at you from a distance. You know there's always a Psycho because of their scream.
Suicide Psychos, another variation, are like normal ones, except they have a grenade in their hand. They are always holding a grenade in their hand, which can be shot and dropped, but it will still explode. Their primary function is to get next to you and detonate the grenade in their hand, killing them and causing massive damage to you.
Burning Psychos are like normal ones, except they're on fire, and their attacks can set players on fire. Also, when they get up close, they can spit fire at you from their mouths.