I was recently giving a screen-shared demo to a media company that makes the vast majority of their revenue from online ads. One of the execs saw the adblock extension button in the browser chrome, interrupted the demo, and proceeded to tell me how terrible I was. Needless to say we did not make the sale.
Lesson learned: When giving demos, open an incognito window since most plugins are disabled by default.
Someone good at their job would have taken the opportunity to find out why you were using the ad blocker and considered the impact on their industry based off your response. It wasn't professional to have such a childish outburst during a meeting, and to interrupt at that. I would think it's possible you are better off in the long run not getting the business.
The next time tell him that you are finding flaws in adblock to help ad companies. If he asks you for more details tell that this is a support 1 yr service because you have a dedicated team constantly researching new adblock versions.
I have a similar anecdote. I work for a company selling a recommendation platform to travel agencies, and the content we display is often similar in layout to regulars ads. It happens, from time to time, to demo a version of their own website to them, with the proper recommendation block injected (mostly to seek the client's validation on the look and feel). And, I recall having one of them congratulate us for the fast loading and clean display of their pages (on my ublock-running-browser). I didn't pick this up. Obviously, the original page was literally cluttered with ads..
Lesson learned: When giving demos, open an incognito window since most plugins are disabled by default.