That's funny, because one of my dive trip failures was to Tioman. I was going up with my instructor for the check-out dives for advanced nitrox and deco procedures. I dutifully showed up at 7:00 am to catch the ferry at the World Trade Center terminal. As you probably know, though, the ferry from Singapore to Tioman leaves from Tanah Merah. (It did back then, anyway.)
I had another fiasco at Tioman when I flew up with no room reservations. My friends told me I could easily grab a hut anywhere. Which is probably true on any day besides the start of Hari Raya (Aidilfitri). Anyway, I managed to find a place after hiking up and down that west coast in 33º heat with all of my gear a few times.
I did a trip to Sri Lanka that was marred by some serious diarrhea. I had to skip 3 out of 5 dive days. I also couldn't eat those days, or keep water in. On the plus side, I did manage the plane ride home without soiling myself--but I wasn't 100% confident of that when we set out.
Diarrhea struck me on a week-long liveaboard in Thailand too, but I didn't miss one dive in a great week of diving highlighted by multiple whaleshark encounters. I was actually sick before the trip began, because I spent the week prior to the trip in Phuket, day diving and, apparently, eating indiscriminantly. The upside? I was model-thin by the time I headed home, and a lovely SilkAir stewardess did her best to pick me up on the flight back to Singapore.