The term Mitzvah has two definitions; doing a good deed/act of kindness and, also, observing a Commandment. 

Not performing a good deed/act of kindness is just that...a non performance of something that is self-fulfilling and, to my knowledge, has no opposite. 

Violating an accepted law "Halachah" or, worse yet, violating one or more of the "Asaeres Hadibreh" - 10 Commandments is called committing an "avaerah" - a sin.