It's actually a joke I'd heard before, and it goes like this:
Two hunters are out in the woods when one of them collapses. He doesn't seem to be breathing and his eyes are glazed. The other guy takes out his phone and calls the emergency services. He gasps: "My friend is dead! What can I do?" The operator says: "Calm down, I can help. First, let's make sure he's dead." There is a silence, then a gunshot is heard. Back on the phone, the guy says: "OK, now what?"
I memorised a joke in Mandarin about 2-3 years ago, and I've got great mileage from it since then - so I decided to translate this one, and will set about memorising it over the next few days. Because of the subtle wording required to make this joke work, I did this yesterday as an exercise with Judy, my Chinese teacher.
In case you'd also like to learn the joke, here it is joke in Chinese. (For an easy pinyin pronunciation of any of the words, here's a shortcut to MDBG.net's version.)
两个猎人在林子里打猎，其中一个突然昏倒了。看起来他没有呼吸，他的眼睛干瞪着。他的同伴打电话叫救护车。他说，“我的朋友死了，怎么办？” 接线生说，“冷静一点，我来帮你。首先确定他真的死了。” 安静了一下，那边穿来了一下枪声。同伴说，“好了，然后呢？”
So what was the first joke you memorised? You're welcome to copy it into a comment below, or at least provide a link if you have one.