Where do you draw the line?

I had a lesson recently where I gave a presentation and encouraged discussion and input from my class throughout the session.

The class in question has a number of individuals who are difficult to engage and who find it difficult to concentrate.  Throughout the presentation, I was faced with bad language, innuendo after innuendo and some degree of disruption.  But.... and it's a big but.... the class did discuss the information required, and they did contribute to the content.

Afterwards, I considered whether I should have been more forceful in trying to stop them from using such language in class, but it was a pay off.  I didn't want to alienate them by coming down too hard, but neither do I want to be seen as a soft touch.  Where is the line between tolerance and weakness?  I think it's a judgement call for each and every case individually.  I hope I got the balance right on this occasion.