What's the point of going to the gym if you don't get to show off all those gains every once and a while? So, turn that oversized shirt of yours into your new favorite gym shirt. Just take a pair of scissors and get rid of those sleeves. Make more cuts to open the sleeve, and you're good to go. You can also add an open back for those harder workout sessions.
This is a great way to make the most out of your current gym ensemble without actually having to go out and spend a bunch of money on completely new gym clothes.