People of culture rejoice! Steam now lets you completely hide those one-handed games from everyone

Full information about the Shopping Cart and Private Games update on Steam
Note that this feature is currently only available to Steam Beta users, which is super easy to become:
Steam->Settings->Interface->Client Beta Participation->Select Steam Beta Update

In short, you can private any game you own, individually, and it won't show to anyone (friend or not). You are the only one who can see it. It even removes the game's stats (achievements from your Steam profile Achievement Showcase), but again, only for those looking at your profile. You still see the same stats as before (which is kinda weird). Anyway, I guess now you can culture yourself without having to explain it to your friends and family.