People take the time to email me directly. Even if it isn't something worth my time ("Hey I see you're doing a startup! How about you quit that and join mine?")

People take the time to email me directly. Even if it isn't something worth my time ("Hey I see you're doing a startup! How about you quit that and join mine?"), I'm still going to respond with "No." Or a canned response. Consider it a personal philosophy — if someone takes the time to email me, I'm going to respond. It might not seem to give much value, but it actually makes me and my personal brand look better. Do you want to appear like a douche by not even deigning to respond?