By saying OMG noone else ever do this costume, this is the best!
Do you realise that words in public are … in public? Do you know how many people you just put off ever even thinking about attempting that costume and how small you actually make others feel.
Do you also realise you are reenforcing negative sterotypes that say we are all competitive by saying there can be only one?
Tell someone they rock hardcore absolutely but stop putting down others in the process.
Edit: and yes I have told people off for using the same but more subdued “compliment” for me. It’s not flattering it really isn’t.