Big game for Reggie over his former team. And thoroughly outplaying his former OKC teammates Russel Westbrook and James Harden. He’s had many battles with Westbrook in the past, he’s had disagreements about his role/minutes/contract in OKC back then.
boxscore: https://www.espn.com/nba/boxscore/_/gameId/401584885
I highly doubt he hates him. There’s possibly just some bad blood from their OKC days where Reggie was getting upset about playing time and they ultimately traded him to Detroit. Steven Adams had a book excerpt a few years back where (and I’m paraphrasing here) he basically said the locker room started to not fuck with him after playing time issues and his insistence on starting over Russ.
Reggie basically said Russ is like a brother to him now. So that beef died ages ago