Not normal yawning, but when you’re with people and sitting having food or drinks or whatever and someone is (genuinely) yawning, again and again. Not a subtle yawn, but a noisy yawn with no attempt to hide it.
Is it rude or can it not be helped?
YABU - it can’t be helped and people should be free to yawn in people’s faces
YANBU - it is rude not to attempt to hide the yawns with your hands and do it quietly, and if you’re that tired you should be away to bed not drinking and yawning