I've spent a great deal of time on Greyhounds, and have never once had an experience unpleasant enough for it to be ingrained in my memory.
In fact, I recall meeting very friendly and interesting people on a number of trips. I once met a charming young lady, discretely accompanied by a pet mouse, on a trip home on a school break; on another trip, I met a Ph.D from Argentina, travelling to a small(ish) town to present at a forestry conference; another time, a young sawmill worker whose lady friend lived in a neighboring town (I recall, he was a very talent chess player). I have many, many friend who also travel by Greyhound, and they've never relayed to me a negative experience either. If a person is not friendly, they'll just go to sleep or read a book.
Rest assured, BarrelWannabe, you have nothing to worry about.