(idiomatic) Not caring at all, being no skin off one's nose, being of no concern at all.

what

anything; whatever one likes

any

painful / イタい: (slang) cringy; embarrassing

What?, Huh?

itchy / to fall ill

(informal or dialect) Alternative form of 痒い (kayui)

itchy, itching

(adverbial particle, dismissive, derogatory) emphasizes disgust, contempt, or otherwise negative feelings of the speaker: whatever