肉包铁 refers to driving a motorcycle because once a crash happened, your body would get hit first rather than your vehicle, so It's yourself who protect the motorcycle instead of the opposite way. 肉 here means the delicate human body while 铁 means the vehicle. 包 here means to cover or protect something. Another phrase comes to mind is 铁包肉 which refers to driving a car. You can acquire the phrase by considering it in another way around.

意思是：一个骑摩托车或者自行车的人（并且倾向于不遵守交通规则，有危险驾驶的行为）。 这个词来源于和 “铁包肉” 的对比。 “铁包肉” 意思是：人坐在小汽车里。汽车外壳是铁，在外面，人是血肉之躯，在里面。所以叫“铁包肉”。

i have to say that's a very good question.cause I think a lot of people in China maybe don't know what it is.it's very simple.which means "Iron wrapped in meat"for example,you ride a bicycle or motorcycle.and"you（你）"means"meat（肉）","bicycle or motorcycle（自行车或者摩托车）"means"iron（铁）".as we all know bicycles are made of iron,that's“肉包铁”. there is another word called“铁包肉”，for example,you take a train or a plane.this vehicle is wrapped around you,that's“铁包肉”. and last,im sorry to use my embarrassing chinglish to explain it for you.I'm very happy to help you!

Thank you so much :)

"打听"这个词，用得好啊~ sounds 100% native :)