Maybe other people have noticed this but, the three protagonists in GTA4 can get angry! Niko Bellic, Johnny Klebitz and Luis Lopez will be in an upset mood usually after you die. After respawning at the hospital they will have a 'pissed off' look on their face. Their dialogue is different as well. They will shout things in frustration if they are trying to steal a vehicle that has locked doors, they will yell rude things at people that they bump into, they will be more verbally aggressive when they are stealing a car from someone, they have more intimidating taunts while they're fighting or pointing a gun at someone.
If anyone else has noticed this tell me your thoughts! If there are other things that the characters act differently with let me know as well!