I have a travel mug I use on occasion, which was given to me a couple years ago. It's nothing fancy, but it does the job. For me, at least. Others who have the same travel mug have complained in the past about it leaking, but it never did that for me. Until yesterday morning, that is.
I noticed that the place I set it down had a wet circle, and the bottom of the mug did indeed feel damp. After finishing off the remaining coffee and letting the mug sit for a little bit it felt dry again. Then I refilled it, and as soon as I picked it up the bottom felt wet again.