I might as well be hanged for a sheep as a lamb

might as well be hanged for a sheep as a lamb

One might as well commit a worse offense, since the punishment will remain the same. (In the past, theft of a sheep was punishable by death.) I've already blown most of my savings, so what's another $100? Might as well be hanged for a sheep as a lamb.
See also: hanged, lamb, might, sheep, well
Farlex Dictionary of Idioms.

hanged for a sheep as a lamb, might as well be

Might just as well be punished for a big misdeed as a small one. For example, I might as well be hanged for a sheep as a lamb and have a third piece of cake-I've gone off my diet anyhow . Already a proverb in John Ray's 1678 collection, this expression alludes to the old punishment for stealing sheep, which was hanging no matter what the age or size of the animal.
See also: hanged, might, sheep, well
The American Heritage® Dictionary of Idioms by Christine Ammer.

I might as well be hanged for a sheep as a lamb

or

I might as well be hung for a sheep as a lamb

If someone says I might as well be hanged for a sheep as a lamb or I might as well be hung for a sheep as a lamb, they mean that as they will suffer or be punished whatever they do, they are choosing to do something really bad. I knew I was going to get into trouble for being late as it was, so I figured I might as well be hanged for a sheep as a lamb. Note: For a long time in the past in England, the penalty for sheep stealing was death.
See also: hanged, lamb, might, sheep, well
Collins COBUILD Idioms Dictionary, 3rd ed.
See also:
  • hanged for a sheep as a lamb, might as well be
  • may/might as well be hanged/hung for a sheep as a lamb
  • might as well be hanged for a sheep as a lamb
  • might as well be hung for a sheep as a lamb
  • hanged for a sheep (as well) as a lamb, (might) as well be
  • be blown away
  • be blown away by something
  • blown away
  • transgress
  • transgress against (someone or something)