Casey Abrams ... Is Now a Dirty, Singing Hippie Person

So, there we were ... giving one of our awesome TMZ Hollywood Tours this week ... when we spotted this dirty, hippie-looking dude playing a guitar on the side of the road with a giant stuffed gorilla.

And then we realized ... the beatnik was former "American Idol" finalist Casey Abrams.

The whole encounter was kinda strange ... a shoe-less Casey scatted his way through a song ... and then laid down on the ground with his giant blue stuffed animal, while waving to the people on the bus (totally nice guy).

We're guessing Casey is pulling the stunt to promote something ... then again, maybe he really did go full Joaquin Phoenix.