As a professional person, you should just nod and smile and do your best not say anything horrible to a former boss you can’t stand. As a regular person, I expect your response would start with the GLARE OF ABSOLUTE DOOMTM and degrade from there depending on your self control and alcohol consumption. It’s probably best to avoid those situations entirely.
Also, get on the good side of your IT people. They have mystical solutions. There are none wise as they.