The victim was shot in the face around 9:20pm Friday on Joliet near Uvalde in southeast Houston.
Police say the victim and his killer were both inside a truck when they got into an argument.
The victim stopped the truck and got out. That's when witnesses say they could hear the men yelling at each other.
According to investigators, the victim opened the door of the truck and the passenger shot him at least twice. He died at the scene. His name has not been released.
The killer took off in the vehicle, which is described as a black two-door pickup.
Anyone with information on this crime can call Houston police or Crime Stoppers.