At some point the inspections had an option to disable them. Either for the project as a whole, or insert a special comment above the offending line that would mute it for that context.
However, in RubyMine 2016.2.3 I don't see that option anymore.
I'm not sure when the option disappeared. Is this an intended change? (If so, why?) If not, is it a known bug? Or some configuration one have to do to get it back?