Insolent derives from the Latin prefix in– (meaning, “the opposite of,” of course) and the Latin root solere, meaning, “to be used to (doing something).” So, an insolent man is literally someone who is used to not doing the things he is expected to do. That sounds pretty insolent to me!
From the same Latin root, we get the Spanish soler meaning “to be used to (doing something)” just like the original Latin root, before the negation. So next time you hear in Spanish, Suelo… (“I’m used to…”) you should think, “Don’t be insolent!”. No one will get the pun other than you, me, and our fellow ForNerds fans.
Note that this has no relation to the Spanish suelo meaning, “ground”, which comes from the Latin solum.