I found this one on the internet, too ... and it's a good thing. The snippet you quoted isn't really enough to get the meaning.
The speaker (Gahagan) was accused of murdering a man - and of sleeping with the man's wife. He didn't fight the accusations - initially. And was very nearly sentenced to die by hanging for the murder. He defended his failure to defend himself by saying that he was vain - he didn't want to admit that he was NOT the type of man that would kill another and sleep with the other's wife. It took a brush with a hangman's noose to bring him to his senses.
- For Teachers