How unacceptable is it to take out your frustration on innocent people?

We are all guilty of this at some point; it’s human nature, I suppose. Just how reprehensible is it?

Let’s say, you’re running late for work to begin with, and then you realize you left your headlights on last night, so your car doesn’t start. [It’s completely your fault, but it’s certainly a frustrating situation.]

You then scream at your girlfriend and blame everything on her (even though it’s not her fault at all), and you keep screaming at her until she cries.

You get to work later (just on time!), you sit down, relax, start working, and everything’s ok. You then realize how awful you were for taking your frustration out on your girlfriend, and you call her to apologize.

Is this sequence of events acceptable, reprehensible, or somewhere in between?

Apology accepted, or not?