by 31.8 per cent at 90 minutes...
So you can only be 31.8% over the limit and you have to watch your mates still drinking beer for an hour and a half.
Come to think of it, in an hour and a half, my liver would reduce my blood alcohol by this much unless I'm clusterfucked - and then it's not going to make squat difference to either driving or a hangover.
Fail.