When you find yourself constantly ignoring a RubyMine warning, you can simple disable that warning and de-clutter your editor. E.g. in my Cucumber scenarios RubyMine underlines 90% of all lines because it does not know about, making the file really hard to read.
You can disable any unwanted inspection by opening
File / Settings / Editor / Inspections and searching for the warning text.
What you disable or keep is up to your personal preference. I personally disable at least the following:
Cucumber / Undefined step(it does not understand spreewald or cucumber_factory)
Ruby / Double quoted string(life is too short)
Spelling / Typo(if your English is good)
You can also disable inspections on the fly by positioning your mouse cursor on the highlighted code and pressing ALT + ENTER. It will list the current inspections and offer to disable them.