For me the worst place I have visited in The Gambia. It was pretty atrocious all over the different aspects of a travelling holiday. From flight to people to market to what to do to the hotel. It's full of bumsters who are far more persistent than your average beggar. It was very intimidating for a 16 year old girl and I wouldn't recommend it to anyone unless you were old and lonely and wanted to be made to feel attractive.
Going to Vegas for our wedding. The local airport was very friendly and accommodating. They let us board first since we had her wedding dress and let us put it in an overhead compartment by itself so that it wouldn't get ruined. Then we get to Houston and go up to the counter. We ask if we can board under the same circumstances and the lady goes, "No, you will need to wait your turn." So we talked about it for a bit longer and she said she won't guarantee a spot in the overhead and that the dress might get ruined. "Oh well sir, NEXT!" I couldn't believe it; I know I was asking for an exception but I figured since the others had done it that it would be okay. Then her cronie comes in and starts chattering about some nonsense. I left and just waited to board and hope we could get her dress on without hassle. So the cronie is still chirping in my ear about something and we board. I am walking past her and just ignore her because I am so annoyed and she goes, "Yea, whatever bro." I almost turned around and clocked her in the face. I wasn't rude at all and just trying to get my wife's $1,000 dress on the plane without hassle. I even said can you let her on and let me on at the end; I don't care. It was awful...I wish I could punch that bitch in her face.
My worst was on a flight from Boston back to Los Angeles in 2002. I went to visit with my friend and we had a layover in Philly. It was raining like crazy so United had cancelled our flight. This was at midnight and they said they could get us on a flight at 6 a.m. They offered to shuttle us to a hotel (which we would have had to pay $100 for) so we could sleep for maybe 3 hours top before having to come back to the airport. So we ended up sleeping in the kids play area with a bunch of other people. Even these little old ladies were sleeping there. I gave up my cozy spot on the cushion mat so an older woman could get some rest. It was really horrible.
I've had quite a few, but my worst was being stranded at the airport because the flight got cancelled. After nearly 3 hours of waiting, we were finally put up at a nearby hotel in the dead of night, only to wake up in a short while to board the next flight! It was a trying time because I had two very young children accompanying me.