[BurpIntruder]

I go with, "What's your name again?". When they tell me their first name, I say, "No sorry, I meant your last name?".

Works every time.

[121789]

No it doesn’t. Everyone with a mild bit of common sense knows what you’re doing

[drb91]

What, they refuse to answer? How rude.

[oh_sigh]

Why would you be asking what someone's last name is, especially by asking "what's your name again?"

[dj43nq]

Neat trick but it shouldn't be the only one you have. Which is to say it isn't the best way to proceed.