Rare drop if you buy enough loot crates.
The scariest thing? I can see it clearly before my very eyes:
"You unlocked ELLY'S THONG 002 (white)"
"You unlocked SEXUAL PRACTICE - FOOTJOB (Ada)"
"You unlocked CUM COLOR 017 (neon green)"
"You unlocked FIGHT BOOSTER x2"
"You unlocked DIAPER-COSTUME (Ada)"
"You unlocked HAIR COLOR 0120 (Emily, brick red)"
"You unlocked THE THIRD OPTION (Sofi's Choice)"
"You unlocked GLASSES035 (Jenna, green)"
"You unlocked ADDITIONAL SCENES (Bathroom Meetup)"
"You unlocked HAIR STYLE 012 (Emily, undercut)"
"You unlocked CHARISMA BOOSTER x3"
"You unlocked NEW PLACE (Preschool)"
"You unlocked FIGHTING STYLE 05 (drunken master)"
"You unlocked MUSIC THEME 04 (Smooth Jazz)"
"You unlocked FUN AND GAMES 007 (bigger asses)"
Of course every single loot box opening plays a long, unskippable and obnoxious animation and a short but far too loud soundbite (a fanfare and fireworks or something), so you get a sense of accomplishment.
Somebody call EA. Here's money to be made AND people to be pissed off...