I haven't done one of these in a while so what the hell, here's a selection of album covers that have bad ideas, bad execution and occasionally bad use of fonts as well.
I do have one disclaimer though. Just because the cover is terrible does not mean the band suck.

 Remember that Black Sabbath, Iron Maiden, Riot, Fates Warning and a host of other great bands all put out CDs with covers offensive to the eyes.

Now read on.   

Profanator - Libido Clerico

terrible metal album cover art
I only just realised that she's supposed to a metal version of  The Virgin Mary
Even before that I just thought this cover was tacky as hell

Toxic Trash - Mundo Doente

Bad metal album art
Illustrated by that well known design studio "The guitarist's Junior-School Niece."  

V/A Detonation (Compilation)

Horrible album covers
This cover is from 1992, by which time people should have known better. 

Hercules Propaganda - Scream For Action

shockingly bad album cover
Now this cover has to be a deliberate "Fuck You" otherwise the universe makes no sense anymore. 

Dwarr - Times Of Terror

You have to wonder if the guy in yellow is supposed to be a specific person and what he did to make teh band hate him. 
It's not the first thing you wonder, I grant you, because there are more immediate questions.
"What the fuck is that thing?" for starters. 

Turbo - Doroste Dzieci

Are the satanic guy down the front and the guy in yellow even in the same band?
Repeat after me: Dungarees are not Metal.
Dungarees are not Metal

Dungarees ...are...not... Metal.

That's all folks.