To beat the boss on level 3, only attack the boss. Equip the Doctrine of Strength, Rope, and Gold so you can not miss your attacks.
Alternate between Head Strike and Slam with Ki power up to make your attack stronger, and use the resist orgasm skill to make sure your attacks hit.
Keep using Will Power to get up when you orgasm, or you'll get a 3rd Lizard appearing, which 3 of them will make Karryn orgasm way too quickly.
Eventually, the lizards will switch to fuck mode and Karryn can dispatch them that way, and the boss should be at 1/4 health. You can then finish him off before going down again. My Slut level was over 150 and I still manage to win, although it was a hour of trial and error.
Question, how can I get Karryn to flash people while working the reception job? I've been trying to raise her up, but it just so slow. I make her drink and fuck at the bar before doing the receptionist job, but no flashing so far as a receptionist. She only flash bar patrons.