I have been in some "bad" motels over the years with traveling for work a lot and riding the bike. but you said worst, so I figured this one is pretty bad as it still stick in my wife and my mind when you say worst motels.
Vicksburg Mississippi. At the time it was a Knights inn. We had traveled all day from south of Tampa bay area and that's how far we made it that day. Place didn't look all that bad from outside, but it was getting dark when we stopped. Checked in, dropped bags and went to go eat. So we get back and its like 7pm or something. Get ready to jump in shower, noticed water was running some and probably for awhile as there was a noticeable stain from dripping water. Took a very long time to get "warm water" Carpet was pretty crappy looking if I remember but I was like "hey I just need to sleep for a few and we are gone". So we get in bed and we must have been closer to a truck stop than I originally thought as you could hear air brakes and such pretty well. Once we turned the lights out there was as much light from under the door as through the window. I had to take towels and shove them in the under door gap to keep out critters and coll air in. Have never stayed in that brand of hotel since. I would have got more sleep at a rest area on a picnic table.