1)A shady or duplicitous
person. A confidence trickster or scammer. A member of a group liable to defraud others - for instance, solicitor, estate agent, bank manager etc.
2)Someone who seems to thrive in an unpleasant environment and always seems to be at the heart of any problems being created.
3)Some it is difficult to prove guilty of fraudulent, unsavoury or similar acts.
Imagine a pile of excrement, with a slippery weazel popping up, looking left and
right while standing up with the excrement on this
head,
like a proud hat, and then disappearing down again.