Although this list is sort of sparse; here are some handy posts I've come across on Reddit:

What are some free online certifications to put on a resume

What's your pic or it didn't happen pic? – maybe not necessarily helpful but def entertaining.

Favorite thing in your 'saved' section? – again not inherently helpful but there are some helpful threads in there.

And here's Reddit's 'Museum of Filth – Although not an Askreddit post, it's very useful to understand some of reddit's ongoing jokes like 'something something 2 broken arms'. Obviously NSFW and NSFL – some of the stuff will make your soul pucker.