S1·E19 Hello? Harmless?

Owen, Alicia and Lolie are aghast when Bob leaves their engagement party for a sexual tryst with Alicia's friend Charlotte - who is herself getting married in a week - and Bob is infuriated by their assumption that he is too nice to go through with it. Trouble is, they're right; and after Lolie taunts him with the fact, it's they who tumble into bed together.