Interesting... I flew United about a month ago too. I suppose there’s some idjits that have been leaving behind some nasty spit-cups. @holes... ruin a good thing for the rest of us.
Some of them, though, like the Camel snus packets you don’t need to spit, and would be hard for them to ever detect, and thusly, care about.
Yeah...I did a little research after I replied to you as I’d dipped on flights for years. It looks like it’s a specific rule of Delta (and a few other carriers) that bans tobacco usage all together in flight. I was kind of caught off guard when the pre-flight instructions from the flight crew specifically addressed smokeless tobacco.