Advice needed, my cousin recently came out as 'gay' last month and his brother keeps calling him a?

poof.....is 'poof' considered a horrible insult, i tell him he should not be so shallow and to stop being so rude and why must he keep calling gay people 'poofs'. What can i do, should i just ignore his behavior...i mean i can't let him go round calling every shirtlifter he meets a poof now can i!