Ask HN: Low performance impact way to toggle block a domain on OS X?

I'm looking to block time-wasting sites temporarily on my work laptop. I say temporarily because frequently i'll browse language specific subs via Google when looking for language libraries that people like, etc. Ie, Reddit does have work applications for me, and i can't purely block it entirely. With that said, i'd love to help break my habit of alt tabbing and opening Reddit.com/r/all any time i hit compile or ran long running processes. Unfortunately my work laptop is very low RAM, and i fear proxies/etc that might slow things down more than i already feel it is haha. What might be a good and performant way to do achieve what i'm after? Thanks!