I've seen many suggestion of RR teams composed of TD characters but most of them were obvious like most of the couples, but now I would like to see something original: Pair up two characters that you wouldn't expect to see competing together, give them a backstory, explaining why they are competing and also how would they interact during the show. I'll start with...

Duncan & Izzy- Runaways:

These two didn't really interact much during the show but the few times they did, the got along very well, so I imagined that one day Izzy got arrested and while in jail she saw a spot on TV for The Ridonculous Race and thought it was the perfect chance to escape but of course she needed a partner and  since she knew Duncan was there she asked him. Initially Duncan didn't want to, but on second thought the travel around the world was perfect for not getting caught and if they won they could've paid their bail. During the competition, at first their interactions would be a bit awkward but later on when Izzy starts doing crazy things that help them going trough  challenges, and Duncan using his skills learnt in juvie, they become good friends and one of the thoughest teams.