What does it mean?
It's so over-the-top that it becomes a joke about desperation: enduring pain just to chase a truck that might carry their dirty underwear.
How to use it
Only among friends who like absurd, gross humor. It's a comedy bit, not a real flirt, and it will creep out anyone who doesn't know you.
How to reply
Save your balls. The laundry truck isn't coming.