Ok, while you are right that this exact scenario (of an entity approaching a dev in a public place while at a conference and asking them to weaken something) does not happen very often, you need to understand that the person you are replying to is saying that in general, it is well known and well documented that various three letters have been active in weakening implementations in all kinds of projects over the years. Remember the clipper chip, Promis, OpenBSD's IPsec stack, NSA_key, or any of the more recent ones we have heard of, and for every one of those there are probably 10 that adhere to their NSL's or other forms of gag orders.
Your snarky and snide tone makes it seem like you think they never try to get people to implement backdoors or weaken implimentations (for side-channels), and I'm sure that's not what you meant, right?
