Cozza is someone you need to run away from. He might chase after you with his little legs. He is a sex offender but you only know this when you get to know him.
Andatoin cozza (Literally "gone taking mussels") is an italian slang term used to indicate a really tired individual, so tired that he/she isn't able to react immediately to questions and events.
(Italian) Frank deve aver lavorato duro! guardalo ora, è proprio andato in cozza.
(English) Frank is really must have worked hard today! Look, he is really gone taking mussels now.