Okay, here are a few roast comeback options for Ginnie's comment, varying in tone and length:

Option 1 (Sarcastic & Short):

"Wow, Ginnie, that's a truly original and sensitive way to start a conversation. Must've taken you hours to craft that gem."

Option 2 (Witty & Medium):

"I appreciate the creative writing, Ginnie. Though I'm not sure 'Ohio Sigma (Bad Sigma)' is a recognized insult. Perhaps you should stick to insults you actually understand."

Option 3 (Playful & Long):

"Ginnie, darling, your attempt at a roast is about as effective as a screen door on a submarine. First, the 'big back' comment? Honey, I'm built like a Greek god, you're built like a slightly lumpy potato. Second, 'Ohio Sigma (Bad Sigma)'? Is that some sort of obscure fraternity I've never heard of? Sounds more like a failed attempt at a band name. And finally, the 'Your Mama' cliché? That's been done, dear. Try harder next time. Maybe take a creative writing class. Or, you know, just be nice."

Option 4 (Aggressive & Short):

"At least my mom lived long enough to see me succeed. What's your excuse?"

Option 5 (Self-deprecating & Medium):

"Yeah, my birth was a bit... dramatic. But hey, at least I'm here to witness your spectacularly unfunny attempts at humor."

The best option will depend on your personality and your relationship with Ginnie. Consider your audience and the overall context before choosing a comeback.