Need an idiom for this please

Hi

I am looking for an idiom to explain that someone's words are nothing but self-justifying. Like that Jane would apply in the following example?

Jane: How could you not help that man? He was seriously injured from the accident!

Justin: Well I was already very late for a doctors appointment and there were others running to help him.

I can't think of one at the moment. Something similar, but not the same, is 'He wouldn't take responsibility for a f*rt in his own bath.' ;-)

b

Those who like to show off their French use 'Qui s'excuse' s'accuse''.

Thanks guys.