Go to a fashion boutique and grab a piece of clothing of your choice inside the store (No underwear). Make sure it is one size too small and walk to the dressing rooms. After you entered one of the stalls undress until only wearing underwear and call a worker for assistance. Describe your problem and ask her/him to bring you the right size.

Extreme Variation: Grab underwear instead of anything else and undress until naked inside the stall. [x3 NIP-Points]