When he uses his middle finger

"Madam, what kind of ring is that you're wearing... Can I borrow for a sec?" my classmate Dave asked the English teacher.

"Sure", she replied, taking off the ring and handing it to him. It was not her wedding ring, so it was just fine for her to hand it over.

I saw Dave putting on the ring on his finger, and I exclaimed out of thin air, "Omg Madam... Dave's using his middle finger!"

Half the class, who don't get my pun, gasped.

But Madam simply continued working with her papers without hardly giving me a notice... Unlike half the class, she realised that the phrase "using his middle finger" may sound similar to "pointing his middle finger", though both are hardly synonymous.