Here's another reminder that if you do a bunch of drugs, your cognitive skills WILL decline . . .

A 50-year-old guy named Marvin Cumberworth tried to return a cell phone to a store in North Vernon, Indiana on Friday.  (About 50 miles southeast of Indianapolis.)

But he forgot he was storing his METH PIPE in the box instead of the phone.  And when employees found it, they called the cops.

Cops tracked Marvin down and found a small amount of meth on him.  Then they found a bunch more at his house, along with about six ounces of pot.

He eventually admitted he sells drugs to supplement his income.  So he's facing charges for dealing.

And he accidentally got his FRIEND arrested too.

40-year-old James Earl was at Marvin's house when the cops showed up, and also had meth on him.  He's facing multiple charges for possession and paraphernalia. 

(Here's Marvin's mugshot and his friend's mugshot.)