It all started when Seth Rogen called Bieber a "piece of s**t" on Twitter following the Baby singer's legal troubles in Miami, but escalated when Rogen took to The Howard Stern Show to explain the two's hilarious in-person encounters.
"Justin Bieber had ... No humility, no awareness, no sense that, 'Since I appeal to young, young people, maybe a grown man who works in comedy doesn't give a sh*t about me? And maybe I should act in such a way that maybe this isn't the greatest experience of his f*cking life to meet me?' And I just remember thinking he's a piece of sh*t," he told Howard Stern in May.
Bieber later responded via Twitter.
"Seth Rogan sorry I didnt bow down when I asked 2 meet u was probably a bit shy and didn't want to be over the top but still. love ur movies," he tweeted.