Here's the quickest, easiest, and non-douchiest way to remind someone to respond to your email:
Send them back an email that says:
That's it! Just reply back to the email thread with the word "bump."
I learned this a while ago from my friend Sungho. Leave it up to an Asian to come up with something so elegantly simple ;-)
The first time I ever saw this "bump" method in action was in 2011 when Sungho sent me a time-critical email......and I didn't respond:
A quick "bump" from him, and the burden once again fell onto me to respond. AND he didn't sound annoying!
So next time you need a time-critical email answered, give it a bump!
Use this trick wisely my friend,
P.S. Share this trick with your co-workers:
P.P.S. Check this out if you wanna see some other people's email open rates.