Looks like T.O. could be tick off:
Definition of tick off
1: to make angry or indignant
the cancellation really ticked me off
The language is flexible enough to allow us to say T.O.’d. This kind of usage is not unprecedented (e.g. K.O.’d for knocked out). We understand T.O.’d to mean ticked off.
It seems to fit, as the plot suggests the characters are deceived:
Total Drama Island is set in the fictional titular reality show, which follows the competition of 22 unsuspecting and unknowing teenagers at Camp Wawanakwa, the most rundown, bug-infested, disgusting island located in an unspecified area in Muskoka, Ontario. The campers participate in competitions and challenges which get more insane and dangerous each week to avoid being voted off the island by their fellow campers and teammates.
They were expecting a 5-star resort, but ended up in rundown dump. Hence, they were T.O.’d, ticked off.
To me, tick off is a milder version of piss off. Also, we sometimes use acronyms or abbreviations to soften or censor a word or phrase (e.g. F off, a steaming pile of S, an M-Fer, that S.O.B.). The usage of abbreviations like this is informal.
I was able to find a clip here (the line in question begins around 2:40). The host talks in an informal, slangy way that appeals or mimics the way teens and young audiences speak. The choice to use T.O.’d here, I think, not only serves to soften the language, but also to sound catchy or slangy (maybe even jocular).
All in all, the usage of T.O.’d makes sense in this context. In general though, I’m not sure how common T.O.’d is, but I think P.O.’d (pissed off) is somewhat common.