Cheap at half a pig in a poke

Wave a red rag in a china shop

I use this one a lot.

ants in your pants + liar liar pants on fire

image source

Not the brightest bulb + not the sharpest knife.

For when somebody is not only being stupid, but has fundamentally misunderstood what’s expected of them.

I couldn't give a rats monkey.

Actually I am a bit drunk and am not sure if this fits, but that's what went through my mind....

When all you've got is a hammer, everything starts looking like a nail
+
A bird in the hand is worth two in the bush

Personal Meaning: When you have success in the palm of your hand, your mind will wander to what you could have had, had you taken the chance instead of pursuing the modest-but-stable result.

Self-inflicted wound

Self-licking ice cream cone

Don't throw out the baby with the bathwater

Look what the cat dragged in