a jar of dirt - a promise of something cool that turns out to be the worst t

a promise of something cool that turns out to be the worst thing ever, like a pizza that's just bread and ketchup

I got a jar of dirt for my birthday and it was the worst gift ever.

My friend said he’d give me a jar of dirt if I failed math, and I did.

My mom said she'd give me a jar of dirt if I didn’t clean my room, and I didn’t.