You will need the bump map enabled underwear mesh for the barbie bodybuilder from
here for these to work in your game.
Here are 24 pairs of boxer briefs for the bodybuilder.
They are organised into 3 sets with 8 pairs of boxer briefs in each set.
Set 1 - normal boxer briefs.
Set 2 - side slashed boxer briefs.
Set 3 - rather daring boxer briefs.
Credits:
Base mesh - Marvine & Beosboxboy