If you’d like to get the T-shirts pictured above for your GTA Online character, all you have to do is log in on the days indicated beneath the shirts. By playing on that day, you’ll get to keep that shirt. This is all a part of the special weekend event to celebrate the new “I’m Not a Hipster” Update.
There are additional bonuses for playing this weekend. Play some of the new jobs from the “I’m Not a Hipster” Event Playlist to earn Double GTA$, and try the new Gang Attacks for 3X RP per kill and Quadruple GTA$ in the Gang Attack Crates. If Deathmatches are more your thing, Kills Streaks and Headshots will earn you Double RP, as well. There will also be Event Crate Drops throughout the weekend.
Rockstar is also hosting several contests, so be sure to check out the official announcement for the full details.