Another joke incident that I'm not a fan of is The Altitude Joke. When a person is jumping on a bin or standing on a chair to reach something etc, another 'joker' will say "don't jump". This joke has occurred  most months for all my working years in a printing factory when on a machine or flattening down a paper skip. This seems to happen as much even when you are raised up on a step of six inches for even more 'comic effect'. 
But as I laugh politely at their comedy prowess like it's the first time any idiot has made such a joke it strikes me that whilst a person is on a ladder five foot above the ground while changing a lightbulb, this is not the time to make that person giggle so much they have tears in their eyes and lose control. So there's a safety issue at the heart of it actually.
This brings me to the other comment that's generated whilst slightly higher up from sea level than usual. There's a type of person who will see you and tell you "be careful not to fall off". 
"thank god that you've told me to be careful up here as I was jumping up and down in a carefree manner totally oblivious to thinking that gravity was about to smash my skull in".
The last van driver who passed me said "watch you don't fall off" to which I replied " careful not to crash and die on the way to your next delivery" 
He didn't seem too happy about my health and safety warning that I'd repaid him, maybe he only liked dishing it out.