Why can't I hide my active application (e.g., Chrome)? This happens from time to time: the "hide" option is just grayed out and the usual shortcut doesn't work. I'm not doing anything special or stuck in a modal window—it just isn't available.
This is OS X default behavior in every app if you have hidden all other apps before with "Hide Others" or ⌥+⌘+H. In such a case it's not possible to hide the front most app, that's why both options are greyed out/inactive.