..."Depend upon it, my dear, that when there are twenty, I will visit them all."

In countless rereads, I've never been able to decide if a)Mr. Bennet is seriously thinking that twenty young men would then be worth visiting because surely a couple at least would marry his daughters; or b)he's just saying anything to end the conversation with his badgering wife.

Also he could be thinking that he'd only visit twenty young men in the neighborhood because only then would it be socially unacceptable not to.