Definition of for all you care (or he, she, etc. cares) in US English:

for all you care (or he, she, etc. cares)

phrase

informal
  • Used to indicate that someone feels no interest or concern.

    ‘I could drown for all you care’
    • ‘The problem is he can't say out loud that for all he cares California can slide into the ocean and become excellent reef material or he might tend to discourage Republicans to vote for local candidates.’
    • ‘Then wear it with rubber shoes, for all he cares!’
    • ‘It could all be done with elastic bands for all you care.’
    • ‘They could be wearing grass skirts for all you care.’
    • ‘Ralph told me that I can punch the punching bag until I drop for all he cares - he really wants me to get this out of my system.’