Shaming your opponent is easy.
All you have to do is find a player during the party, on the street or anywhere where it is possible to showdown with one. Then showdown with that girl. Win. Showdown again. Win. Repeat until her confidence runs out completely. It will take you around 5-7 showdowns to shame your opponent.
During the final showdown you will receive 3x xp and cash from your win.
If you are at a party the girl will even flee in shame!
TIP: To showdown and win every time plus use less confidence, change first into the lowest hotness outfit. Go to Tokio Harajuku, for example. Go into your closet again and change this time into your highest hotness outfit. Showdown!