1. Someone who tries to appear modern (hence "mod") and trendy by dressing in fashionable clothes. He spends so much time and money on his appearance to project this hip façade, but he's just a mod poser.
2. Someone who pretends to be a moderator, or acts as if they have the authority of one, in an online forum or community. I was playing against this guy online last night who was a total mod poser—he kept threatening to ban my account just because he kept losing to me.
mod. contemporary and fashionable in clothing and ideas. Your clothes are mod, but you’re just a plain, old-fashioned prude.
mod poser(ˈmɑd ˈpozɚ)
n. someone who looks mod in dress only. (Collegiate.) Tiffany is such a mod poser. At home it’s jeans and a T-shirt.