Someone I know does this, and seems to think it's a flex, because he bragged about it being "the first time I've actually seen this presentation" a few times during the presentation.

It was all awful.

I feel like we need to normalize walking out of meetings like that. If you have no idea what you’re presenting why is anyone in the room?

At my previous company, a distinguished engineer did this. Used generated slides he hadn't looked at until presenting to the entire staff+ engineer group. The slides weren't good and he mostly ignored them.

I would immediately stand up and walk out of there. That's my time you're wasting!

“I came in unprepared. Please hold your applause.”