Apparently they had too much trouble with people disposing of their gum under tables, on elevator buttons, in mailboxes and even inside keyholes. As a result, in 2004 they banned its importation and consequently you can only get chewing gum with a prescription from a doctor or dentist. Supposedly a black market has yet to emerge, but I can’t verify that.

I learned about this fact from: http://en.wikipedia.org/wiki/Chewing_gum_ban_in_Singapore