Deposit here

What is the hardest thing known to man?  Some of you might reply "diamond," but you'd be wrong, the hardest thing known to man is dried bird shit that has dried on the surface of your car and is impossible to remove.  It is certainly harder than concrete and will probably take a diamond drill to remove it, except that it's harder than diamond.

My parking spot in our car park is under a tree, and the birds gather there in order to target my car.  I hear them calling to each other, in bird-speak, "come one and all, come over here, and deposit your offerings on Jack's nice shiny car."  At least it used to be nice and shiny, but now its an amazing conglomeration of dark brown, light brown and white droppings.  They especially like to target the door handles and the windshield.  What have I ever done to them?

A helpful car cleaner told me that baby tissues, soaked with rubbing alcohol, are the best thing for taking them off.  Its true they do work wonders, but there are so many droppings and they are so hard, you find yourself wiping them vigorously for a half hour and getting nowhere.  I used to enjoy nature, now I've learned that bird do-do is a fun part of it.  

What is the hardest envelope to open, yes, the one that has perforations all around it.  Of course the perforations are added supposedly to make it easier to open.   But, in fact it works the other way.  A simple envelope that can be ripped open in a second is not good enough anymore.  You have to have perforations and then inside there is a kind of gum that cannot be separated, but that tears the paper so that the contents cannot be read or identified. 

What is the hardest thing to say, admit you were wrong.  Have I ever made mistakes?  Certainly I have, but to paraphrase Frank Sinatra in "I did it my way," "Mistakes I've made a few, but then again too few to mention."