I was wondering how do you save a right tricep texture?

Define save it? do you mean the file?
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If so your custom folder will house all your and your opponents textures, C:/games/Toribash 4.2/Custom/(you or your friends folder)

Like how do you save it. Isn't it like r_tricep.png?

You can save it whatever you want.
Just upload it.

Names of all body parts:
head
breast
r_axilla (part of torso)
l_axilla (part of torso)
l_biceps
r_biceps
l_triceps
r_triceps
l_hand
r_hand
chest (part of torso)
stomach
groin
l_butt
r_butt
l_thigh
r_thigh
l_leg
r_leg
l_foot
r_foot

Taken from this guide: http://forum.toribash.com/showthread.php?t=28309

Thanks!