As per this "old joke", told in a discussion of ways to stay fresh on long connecting flights:
There is an old joke that I use about my quick baths at airports. I strip down to my underwear and while standing at the sink, I wash down as far as possible. Then I wash up as far as possible. Then I go to the stall and wash possible.
I encountered this via the comments to this https://travel.stackexchange.com/a/90443/4188 answer, specifically. Reproduced below.
As you say, the best way to avoid being that guy is to try and wash yourself in between flights. When showers are not available, you can use (scented or unscented) baby wipes to clean your armpits and other exposed smelly body parts. You can wash your face and neck in any restroom sink. And don't forget to brush your teeth. Changing shirt/t-shirt is also very helpful.
- This answer led me to this flyertalk thread -- apparently there are (much) better solutions than just going with baby wipes for this kind of non-shower. – chx
- worth it for the rerun of the "wash possible" chestnut, @chx – Kate Gregory