Boomer is used to refer to someone who was born during the years after the Second World War, often to suggest that members this group are selfish and out of touch. It is short for baby boomer. [informal, often derogatory]
His essential point is that boomers are selfish to the core.
When challenged by her older colleagues, she simply snapped "OK boomer".
The boomers benefited from growth in housing wealth, generous state provision, and long retirement.