The first and only thing to remember at a bachelorette party is that you are there to celebrate the bride, period. So everything you do and say should embody that good intention. That translates into not talking about her awful ex-boyfriend (via WeddingWire).
It’s bad at any time but especially if her heart was broken over him. No “look what he’s missing” because that will force her to think about him instead of her new life. No comparisons to her current fiance either, even if said in jest.
It’s also not a good idea to tell the bride to do anything that makes her feel uncomfortable, including strippers or flirting with others. Don’t tell her that she should go dance or hook up with some cute guy. Not only may that go well beyond her boundaries and be considered cheating but it will put her in an uneasy situation, and in a worst-case scenario may even jeopardize her upcoming marriage.