Most absurd - all of their teachings regarding the flood. They teach that: Noah actually existed, and was as old as the bible says he was. Nephilim were real. The earth has a vapour barrier,or "water canopy" around it. Animals were not mean, and didn't eat meat. Neither did humans. Noah preached about Jehovah and the coming flood when he wasn't busy chopping trees down and building a 450 foot long boat. Which in their paintings is the shape of a chocolate bar. Jehovah then had two of EVERY species of animal on earth come and fit into this boat. The flood waters came, covered all of the earth even the highest mountains. Noah still did Family Worship on the ark.
Oh, and this was only 4500 years ago.
They teach all of these things as fact, they even still have articles and talks about it. Even the water canopy thing and that animals didn't eat meat. Wow.
Not their most absurd by impossibility, but most harmful would be the blood doctrine. I cringe when I wonder what could have happened had I or someone close to me been seriously injured and needed blood.