Looking for a word

A 'couch potato' is a term for a lathargic person who is not associated with any form of aerobic activity.

Layabout
Lazy-ass

my mom always called me a vegetable.

a bum

Slacker.

"lump"
"slug"

"Flaneur."

OK, to sort these...

"Layabout" and "lazy-ass" (noun and adjective respectively) are used for someone who is expected to perform and simply neglects to do so.

A "vegetable" is someone who, through some disability, is incapable of significant movement and thought. carriegood's mom was using it in a hyperbolic way, just joking.

A bum is, strictly speaking, a homeless beggar who wanders around asking for handouts and sometimes is willing to work in return. You mostly hear it spoken as, "You lazy bum," where the speaker is comparing his target to a good-for-nothing vagrant loser.

"Slacker," my personal favorite, is a newish word used by younger people to refer to someone who just never tried very hard to do well for himself in the first place.

"Lump" and "slug" are old (but still good!) words that a Renaissance speaker would completely understand. They just compare the target to something slow, dull, and useless.

"Flaneur?" Is that English? I don't think that's English.

Goldbrick or goldbricker. May be military in origin, but once commonly used to describe someone who didn't "pull his weight."

deadbeat, goof-off, lazy-bones, drone, drag, waste, shlep, good-for-nothing, lounger, slouch

"Deadbeat" is my favorite. Although it can be used to simply mean "a lazy person," it is often used to refer to someone who doesn't pay up.

"shlep" doesn't belong in the list of laziness expressives. To "schlep" means to move from one place to another, usually carrying something unwieldy.

I think the word wanted is "schlemiel."

And drone means to make a low humming sound. And slouch means to droop into a relaxed posture.
And drag means to trail along on the ground.
And bum means buttocks.
And vegetable is something you eat.
And lump is a mass.
And slug means to hit, or is it a slimy mollusk?

Yes, schlep or shlep is also a verb. But still, we are talking about slang. In various regions, slang differs. Where I come from, shlep is an insult meaning lazy person or deadbeat.

A "schlemiel" is more of a stupid person... unless it is used to describe a lazy person in your region, Speedwell.