An insult you call someone who sucks. Doesn't mean much but also means anything you want it to. A girl in my dream called someone else a Seth and she was pretty mad so it seems like a good insult.
"You are such a Seth"
"Stop being such a Seth"
Someone you don't like. Isn't a specific insult but a broad term for an annoying person
"Okay Seth"
"Omg you are such a Seth"
"I know y'all are dating but she is such a Seth"
"I can't believe he gave us Homework over break, he is giving big Seth Energy"