Will Smith who plays Deadshot in Suicide Squad, spoke on Jared Leto who plays The Joker during an interview with Beats 1, stating that Leto was all in during the filming of the movie.
“I’ve never actually met Jared Leto, we worked together for 6 months and we’ve never exchanged a word outside of ‘Action’ and ‘Cut’. We’ve never said ‘Hello’, we’ve never said ‘Good day.’ I’ve only ever spoken to him as Deadshot and him as the Joker. I literally have not met him yet. So, the first time I see him will be ‘Hey, Jared. What’s up?’ Not a single word exchanged off camera. He was all in on the Joker. I’m looking forward to meeting him.”
Listen to Smith talk on it around the 15:40 mark: