Now I know that most people in a triathlon use a gasp bicycle to ride out thier bike portion. I was wondering, and if its ‘legal’ to ride a coker in a triathlon? If so, this might be something I might consider pursuing eventually. I know hydration would be something that would have to be worked out, but what sport doesn’t have problems like this? I just looked at a brief outlook on the rules and nowhere in there does it say you can’t have a uni, nor does it say you can.
I say you should ask the people who hold/host these triathlons. If they say you can, then do so. IMO this seems to be the best way to find out. 
I rekon it would be a great idea just dont expect to position well because I dont think you will but yeah if your allowed would be great!
why wold you want to ride a unicycle?
they are slow and inconvenient.
They’ve been used in multi-stage adventure races, which are kind of like triathlons.
It would at least go against the typical triathlete style of buying the most expensive bike in the shop, setting it up really stupidly, and riding like your granny. You’d have a good excuse for riding like your granny if you were on a unicycle.
Personally I’d not bother, traithlons are usually super expensive to enter, and the bike courses completely utterly soul destroyingly boring.
Joe