To essentially wipe the mind of all sane thought (and likely replacing with insane thought, though not necessarily so), presumably from an encounter with something so incredibly insane as to have the power to do so.
This process is similar to sanitizing, but instead of removing dirt and/or germs, it removes rationale; thus, insanitize is an effective portmanteau of the words insane and sanitize.
"Don't pay attention to what he says, or he'll insanitize you with his stupidity."
{origin of phrase}
"So I was having a discussion with My Mother. The rest of the details are unimportant, logic and reason are the exclusive domain of the man." "Whut, what prompted this? Did I miss some epic fucktardation or something?" "Yes, yes you did. Be glad you didn't see it originally. This mirror alone will surely insanitize you."
cool man: "ey, u see insanisite over there?"
cooler man: "wait what i thought her name was notdootlez what the heck"
cool man: "yeah it is, its just her other username stupid"
The suggestion that you need to wash your hands, and wash them again, specifically with a product that no longer exists, until you become insane with anxiety.
She had scrubbed and scoured her fingers and palms until they were raw, her bottles had all been emptied, and she was on the edge of crazy, needing to find more hand insanitizer.