I'm (dietary) fructose intolerant. That can suck too. Especially nowadays when every company thinks it's easier to advertise something as healthy when it is sweetened with fructose instead of glucose (it's natural, it has to be good!), and other companies increase their sweetening by using mixed fructose and glucose (HFCS e.g.). Luckily this kind of intolerance is based on the ratio of fructose to glucose, so most stuff sweetened with HFCS in Germany (which usually contains less than 50% fructose) is tolerable. Most American stuff with HFCS (in Germany most notably important drinks like Mountain Dew and stuff like Canada Dry) gives me trouble though.
Also I have a tendency to forget about this. Really bad: Drinking half a litre of apple juice before realising that it probably wasn't a good idea.
Edit: I just found this sentence on the English Wikipedia article: "This can cause some surprises and pitfalls for fructose malabsorbers."
"Surprises and Pitfalls" sounds a little bit cynical…