How to completely, utterly, disable spell-check on OS X Yosemite? With the kind of writing I do, 99 out of 100 spelling "errors" aren't errors at all. Spell correction is simply incredibly unhelpful for me. I hate the distracting red dotted underline that appears in my native Mac apps.

What system settings can disable this?

I've tried unchecking the available dictionaries, and changing the auto-choose-language vs. specify language ... all through the preferences panel. But even though I've unchecked US English, the system still spell checks automatically with it in apps.
Right-click or control-click in the field where you're working and look at the Spelling and Grammar submenu. You can also disable the various substitutions from that submenu.