Since I hadn't noticed the smutty joke in this text, I started googling this and found a forum where they were discussing sexual references in JAs novels. Apparently there is a book about just this topic called "Austens Unbecoming conjunctions".

They mention as a further example of a sexual pun:

"..In P&P, Caroline Bingley, after paying Darcy all kinds of compliments, with no success, changes tactics. She offers to mend his pen and boasts, "I mend pens remarkably well." I couldn't help being reminded that, in old-fashioned French slang, "mending a gentleman's pen" is practicing a fellatio. No one says that anymore, of course, due to the obsolescence of quills, but it was still in use at the turn of the 20th century. So if JA was familiar with French slang, it would give Miss Bingley's offers of service a very explicit meaning."
Mr. Darcy's response is "Thank you -- but I always mend my own."

I must say I am all amazement.