T-shirts may seem trivial but they're a way to customise your character and may have pointed to a new Grand Theft Auto Online DLC.
There's also a newly discovered glitch which allows you to access t-shirts from as yet unreleased DLCs.
Start a single player game when jump into GTA Online, you need to being in single player for this work. Have an open character slot, if you use a slot with a character in it, you'll need to delete the character and start over.
Once you've created and named your character, do the tutorial. This is necessary in order for the glitch to work. With that done, switch back to your main GTA Online character and then switch back to the new character you've just created. You'll then be asked if you want to change your character's appearance, on PS3, tap the PS button on the DualShock 3 and log out of PlayStation Network.
On Xbox 360, either turn off your wi-fi or disconnect your ethernet cable. This will cause the game to send you into story mode then press start, go to online and select choose a character. Pick your primary GTA Online character and you'll be allowed to alter that character's appearance, confirm that you want to and alter the sex of your character.
The glitch then kicks in and unlocks the DLC t-shirts. Save your settings and you're good to go. With your new character, go to the nearest discount clothes store and buy a bunch of clothing and then the new tops will unlock.
It is then possible to keep the shirts and revert back to your character's original sex. The whole process is explained in the video below.
YouTuber NoahJ456 has also posted a video looking at newly released screenshots which hint at a retro themed DLC for Grand Theft Auto Online. A series of t-shirts for radio stations in past games. It's not clear whether this DLC was scrapped or could still be on the way.