1. something has no effect on somebody
the criticism is water off a duck's back to me
This expression is based on the literal characteristic that duck feathers have to resist water, and is used figuratively in relation to somebody's ability to resist insults, criticisms, or other negative verbal attacks. It does not apply to physical attacks. It can be used in both a social or professional setting, but its informality makes it more common in the former. A similar expression is 'no skin off my nose.'