We had this discussion just the other day - I am the Designated driver so its much easier for me

Could you possibly say you've caught a nasty bug going around and have been having gastro/vomiting? He had severe stomach cramps too

DF had this tummy bug all last week so it was good for Xmas when I had to avoid all those foods you *shouldnt* have like prawns (as hard as it was tho!) so that was easy to fake!

Good Luck!