本应该做而未做 should have done sth.
例句：I should have killed you 5 years ago.我5年前就该杀了你.
本不应该做而做了 shouldn't have done sth.
例句：I shouldn't have kissed you.我不应该吻了你. 本应该做而未做 should have done sth.
例句：I should have killed you 5 years ago.我5年前就该杀了你.
本不应该做而做了 shouldn't have done sth.
例句：I shouldn't have kissed you.我不应该吻了你.