When people get drunk/high and do/say stupid/hurtful/destructive things, do you forgive them because they 'weren't themselves' or are you just irritated that they lost control of themselves in the first place? Does whether or not you similarly over-indulge have any effect on your reaction?
A few scenarios as food for thought:
a) Friend insults you personally and seemingly intentionally.
b) Friend breaks a vase/CD/window.
c) Friend kisses your significant other.
d) Friend punches you.
e) Friend vomits all over your nice new persian rug.
As an over-indulger of alcohol on a quite a few occasions myself, I have to say something that will cause other abusers to call me a liar.
When you use/abuse alcohol or drugs, you know what you're doing at the time. You may not be able to restrain yourself because you've released your inhibitions, but you know what you're doing.
Hitting things, puking, etc. caused by your inability to adequately control your muscles, reflexes (including gag reflex) is a different story. I can forgive someone for that, but not the other things like verbal or physical abuse or kissing someone that you shouldn't be kissing. You have enough sense, no matter how impaired you are, to know that what you're doing is wrong.
If you get to the point where you don't know, you're either unconscious or pretty close to it.
Maybe I have a biased viewpoint since I don't drink, but I think that a person should always be responsible for their actions, unless they have some sort of mental disorder that causes them to think irrationally or to not be able to think about their actions (schizophrenia, night terrors, etc). Drinking a beer, or two, or three, or any other type of alcohol, is a choice that should be used wisely. Anyway who is prone to insulting people when drunk, or making out with other people's girlfriends should not be getting drunk in the first place. If we forgive drunk people for doing small things (insulting others, breaking things, punching, etc), then why shouldn't we forgive those who get drunk, get behind the wheel of a car, and accidentally kill someone? It shouldn't matter whether they're "not themselves"; they chose to drink, so they need to deal with whatever consequences come from their actions.