Whenever I visit the lavatory onboard in mid flight, I always have an urge to clean up the area around the sink, especially if someone left it all wet! A few paper towels and it's all tidy in no time. I also clean the mirror if it's dirty. ^
On a Lufthansa flight from LAX-FRA (op-upped to F

) last month, while visiting the huge bathroom (full length mirror and a window!) I was amused by a little sign below the mirror right above the sink (in English and German):
As a courtesy to the next passenger may we suggest that you use your towel to wipe off the wash basin. Thank you.
My those pushy germans! lol.