A popular idea or statement passed around within a subset of the population as if it was factual, but for which there is no supporting evidence. A fusion of "gibberish" and "wanking".
The idea that most unemployed people are lazy pot-heads is just gibberwank spread by uber-conservatives.
A wanker who is talking gibberish.
George Bush was the most notable gibberwank of the early 21st century.