Who Gets What?

Who Gets What?

Often one hears the compliment, "...so-and-so really gets it."  Or the converse, wherein some person or monolith is judged as less than worthy or clued in, and it is noted that it or they, "just don't get it."  So who or what gets what; just what exactly is the it that is or is not gotten?  And what qualifies as "getting it" and who or what are the arbiters deemed capable of bestowing "getitude" upon others?