You're high off the mountain of coke. Your sister just died and Sosa's men are invading your home, you're pissed! You grab your best gun, a M16 A1 with a M203 40mm grenade launcher. You're ready to go out in a blaze of glory.
Tony knew he was going to die, that's why he said "I'm coming" to his dead sister. That's why he constantly yells out "I'm taking you all to hell with me." He knew it was his final standoff.
You wish you could tell Tony, "look out behind you," but it's too late. "The Skull" blasts Tony in the back with a shotgun and we learn that Greed can lead to your own downfall.