The walls were so thin that one time my coworker who was also traveling heard his phone ring and reached for it in his pocket, but then realized that it was in his room still and he was halfway down the hall already.

It was a newly built hotel too. There's no excuse for it being so crappy. Sound deadening between rooms has very easy solutions - they just cost a bit more (thicker drywall, offset the studs, other things). Whatever they did when they built this place they must have cheaped out so much that it had less soundproofing than your normal residential construction.

This one was a Home2Suites - I don't stay in those anymore.