Rehabbing rock star Steven Tyler treated a bunch of shoppers at a Home Depot to an impromptu concert this weekend -- by singing two of Aerosmith's biggest hits a cappella over the store's loudspeaker.

TMZ spoke to multiple employees at the H.D. in Rancho Mirage, CA., who tell us Tyler randomly picked up the microphone on Saturday and belted out snippets of "Dude Looks Like a Lady" and "I Don't Want to Miss a Thing" for all the weekend warriors to enjoy.

And get this: We're also told Tyler took a hit from a helium machine and kept singing Bee Gees style while signing autographs for anyone who asked.

Coolest. Guy. Ever.