I'm pretty sure if you were wasted, somebody would still argue that had influence in court... and if it goes to criminal court, you may very likely win. However, that opens you up to civil liability and that is where you are likely to "lose" with all the scum suckers lurking about for any chance they can get... but that's always the case isn't it!Obviously this is exceptional to the matters I mentioned, which involved being out and about. I don't think use of alcohol would have any bearing on a legit self defense issue in hour own home.
I would mostly be concerned with how much alcohol the individual can ingest and still maintain accuracy... YMMV