"The origin of the expression go pound sand is from a longer expression, not to know (have enough sense to) pound sand down a rathole. Filling rat holes with sand is menial work, and telling someone to pound sand down a hole is like telling them to go fly a kite. The expression dates to at least 1912 and is common in the midwestern United States."

One who has been fully vaccinated for the COVID-19 virus and brags about it.

To tell someone that what they want isn't going to happen. The concept of pounding sand is to do something pretty useless. You can hit sand all day long, it doesn't change at all. So by telling someone to "pound sand" you are telling them that they will never get their request.

A phrase meaning to “fuck off” or to “go cry about it”.

To order someone to go away or "get lost." This is a widely used term that has no vulgar connotations.

to tell someone to fuck off.

A term used when annoyed with a person.