Examples:

• Why do you knock yourself out for this girl?
• Knock yourself out, I need a night in!
• But I'm trapped, so knock yourself out.
• Knock yourself out and your teeth.
• Oh, knock yourself out.
• Yeah, don't knock yourself out.
• Okay, sure, knock yourself out.
• Don't knock yourself out.
• So, knock yourself out.
• And if you believe these people, knock yourself out. I don't believe a word they say.