I was with a buddy who took me into the United Club as a guest and we were watching the goings on while we chatted and we watched a Gentleman start to fill up a mug with some sort of chocolate covered cookie thing (maybe Graham Crackers??) and then just walk out of the club with the filled Ceramic mug.
Was sort of awesome, anyway fast forward to my flight and Ceramic mug dude is my seatmate and I said to him, "I have to ask, what is with taking a mug from the lounge, I am not about to report you, but I am curious".
His answer spoke to this thread, United is trying to save money by not offering me a disposable cup that I can take with me, so I will cost them more money by taking a ceramic mug. Apparently he has done this a few times as he said that he now has a collection of United Club mugs at home as he travels weekly. I said more power to you and that was basically the end of the conversation, he put on his headphones and proceeded to play on his phone.
BTW, I have a sense that he was a high elite as the Flight Attendant offered him a meal choice before anyone else in the cabin.
Personally, I could care less, the coffee was not so great in the club and the food offerings were not up to DELTA's level especially at certain clubs now where DELTA is offering hot food gratis. As for taking alcohol, I have been known to order a beer and then pour said beer into my water bottle, United's beer is not worth the effort.