He gives a rat's arse about what other people think.

He gave a rat's arse about what she thought.

He has never given a rat's arse about anyone else's opinion.

I am giving a rat's arse about what he thinks.

He worked his arse off to finish the project on time.

Dealing with difficult customers can be a real pain in one's arse.

Arse-end Charlie is a derogatory term used to describe someone who is considered to be at the bottom or lowest rank in a group or organization.

He likes to sit on his arse all day and do nothing.

He is sitting on his arse all day.

He sits on his arse all day and does nothing.