Coke not pepsi, are you talking about any short sleeve shirt over any long sleeve shirt? The original thread was started specifically with regard to tight Lycra long sleeve shirts, which is an entirely different issue.
Personally, I don’t see anything wrong with wearing a Lycra shirt as long as the shirt on top is not too skimpy. As someone mentioned before, the Lycra can cover the sleeves, but if there is nothing over it in the chest area, that is clearly a tznius problem. Then again, if you have a loose-fitting long sleeve shirt, you can wear pretty much anything on top of it. It’s more a matter of personal preference; if you don’t like the style/think it looks ugly, that doesn’t automatically make it untznius.