I think Josh was just spoiling for a fight with Bert and used Bert mumbling an obscenity in frustration (and directed at the computer/printer, not at any other designer) to start one. I also found it strange that Josh would go off about how using foul language indicates stupidity, but yet doesn't seem to understand that throwing huge, public fits doesn't speak well of someone's maturity or intelligence either. Honestly, has there ever been a season of PR where someone hasn't had to be bleeped? He should have known going in that it was likely that someone might occasionally swear because they were tired or annoyed or whatever. Really, his teammates seemed more upset by Josh blowing up than by Bert cussing under his breath. If it's really a big issue with Josh, Josh could have taken him aside nicely and mentioned it. Bert seemed unaware that he'd even said it, and sometimes people honestly don't realize they've been offensive. Bert's exhibited attitude problems before too, but he really wasn't the one who was out of line last night.
And yeah, it's nice of Josh to apologize, but it would be nicer if he realized he wouldn't have to apologize so much if he could control the nasty remarks. I'm not big on foul language either, but I'd take Bert cussing out a computer over some of the hateful things Josh said to and about Becky and her designs.