“Yeah, I'm dead serious.”
You were having a friendly disagreement with your friend about who's going to win a baseball game. You said that you'd bet $100 that the Mets would lose. Your friend asked if you were serious about the bet. You are, so this is your answer.
Yeah, I'm dead serious.
"Yeah" is a more casual way of saying "yes".
Say this to agree with something that a person said:
You can also say "yeah" when you're going to disagree but you want to make your disagreement sound a little softer.
"Yeah" sounds less formal than "yes."
"Dead serious" means "completely serious". You use this phrase to express being very serious about something you said. It's a good response when someone says they don't believe you:
A: No way, man!
B: No, I'm dead serious!