*peeks at the join date* I'd guess you're old enough not to have one of those newbie skins that come with the shirt as part of the skin?

The obvious and easiest suggestion would be to try rebaking (Ctrl-Alt-D for the Advanced menu... then Advanced / Character / Rebake Textures... or Ctrl-Alt-R).
If that didn't help, there's a long way around that helps as long as your skin is copy... some of the steps are redundant, but even though you can skip some of them, the entire set usually helps everyone

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* find somewhere where you can be naked and take all your clothing layers off (attachments are fine)
* wear another skin, if you don't have one, grab one of the default ones from the library
* left click on your regular skin in inventory and copy it (Ctrl-C)
* make a new folder (so you can tell the copy apart from the original) and paste a new copy into it (Ctrl-V)
* Edit / Preferences / Clear Cache and relog
* wear the new *copy* of the skin
* click your heels together three times, think good thoughts and rebake

That generally helps most everyone I've come across with the problem

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If the skin is transfer, but mod, you can try adjusting one of the sliders and go through the same process (obviously you can't copy it then), but I'm not sure if that would help.
If it's transfer and no mod, you could try giving it to an alt, clear cache, relog, get it back and wear, but again, that would be a guess. I never met anyone with a transfer skin who had that problem.
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If nothing helps you can always contact the seller and ask for a replacement.