Can you legally withdraw money from a joint bank account that you did not deposit?

If the bank account is in your name (ie it is a joint account with your name on it) then you have the right to withdraw funds from it or to deposit funds into it. However if you feel that you should not be withdrawing money because it will upset the other person who jointly owns the account then perhaps you should discuss this with them before you make the withdrawal - there is more to life than the simple legal niceties.