Today though, this wasn't the case.
The reader's digest version:
The scene: The party (This is D&D 3.5) has vanquished a group of undead. The druid, their only healer, lies on the ground at -8 hit points. The ranger has stabilized the druid. They're still in the dungeon.
Mage: Hey, Bard! we need your healing potion to heal the druid!
Bard: Oh, I don't know, he's stabilized isn't he?
Mage: We don't have time for this. He's our only healer.
Bard: I totally bought that potion from you, remember? trade me something for it.
Mage: What? That's retarded.
Bard: oh, how about the ranger gives me his ring of protection and I give up my potion.
Ranger: No way!
Mage: Okay, you know what, we don't have time for this.
The mage casts magic missile on the bard, knocking him out. The party gets the potion from the bard, uses it on the druid. The revived druid then heals the bard.
Bard: What the hell was up with that magic missile?
The bard draws his weapon and goes to attack the mage. The Rogue jumps in between them.
Rogue: Okay, we can settle this later, okay?
Bard: No way, I'm going to stab him with my rapier!
Mage: Okay, look, how much would it be worth it to you to just let this drop?
Bard: Uh, how about a healing potion?
Mage: How about a scroll of Identify?
Bard: ... Hm. well, ok.
That's pretty much the synopsis. Add some angry words here and there and you got it. Ever had one of those happen in one of your games?