Post Malone proved he can read a crowd ... busting out an awesome custom tee honoring his late pal, Mac Miller, which got concert-goers on their feet and 100% amped.
The singer was performing Monday night at the PPG Paints Arena in Mac's hometown ... and he came out wearing an oldie but goodie that was custom-made to pay tribute to the rapper -- who tragically died of an overdose about 2 years ago.
It's a white T-shirt that's been decked out to read "RIP Mac Miller" with super-dope designs and airbrush lettering. Post originally started wearing the shirt shortly after MM passed.
Sounds like it was a good move to don it yet again in the Steel City, 'cause we're told the audience went crazy -- the energy in the place exponentially jumped, especially when Post and his shirt got splashed across the big screen monitors behind him.
The crowd was definitely into it -- you can hear them helping Posty sing along to his own tune ... even though it doesn't appear he attempted to cover a Mac Miller song while up there. Probably better that way, no one could do it quite like the man himself.
Of course, Mac's death affected PM immensely ... we got him out not too long after and he was pretty emotional on camera. Good to see Mac's still in his thoughts.