How do I block a website from myself?

I know there have been similar questions posted about this, but they don’t respond to my specific needs.

If you do a Google search about blocking websites, you get lots of advice for parents who want to filter porn and stuff like that.

That’s not relevant to me. I’m an adult, and I’m the only one who uses my computer.

I also don’t want to make it totally impossible to access the website. I would just like to discourage myself from using it.

Think of someone who wastes too much time on Fluther and wants to stop from checking it every day. But this person would still want to have the option to post to Fluther if they really need help with a question. The website I want to block is not Fluther, but it’s a similar site.

I use a MacBook Pro. I’ve been using Chrome for my browser, though I use other browsers too. It would be even better if I could also block the website on my work computer (a PC using Internet Explorer), though that’s not necessary.