A cluster offender is a person who has an incredible ability to offend a large mass of people at the same time usually without any knowledge of what they're doing.
This can often be observed at important gatherings such as parties, weddings and funerals.
(At a wedding)
You: Unless a woman carries my bag for me then she won't be compliant and therefore wont suck my cock
Sally: You're an ass
Pauline: Oh my god you're a cluster offender, we're leaving