Encountering former, abusive advisor at a conference
This doesn’t answer your explicit question, but have you considered sending an email to the conference organizers asking for your poster to be reassigned to a different part of the poster presentation area so that it’s not right next to the former adviser’s poster? This could go a long way towards minimizing the possibility of trouble, and will probably make it easier for you to handle the task you have set yourself of overcoming the anxiety you have related to meeting him at the conference, while leaving you some wiggle room to maneuver in case that turns out to be more difficult than you expected.

The email doesn’t have to go into details, just say this is a person you’ve had some conflict with in the past and you would prefer for your poster not to be close to theirs. If I were an organizer I’d be more than happy to accommodate such a request. 

Good luck, I hope things go smoothly and that you’re able to focus on sharing your work with others and having fun.