It is a truism
You can pick your friends and you can pick your nose, but you can’t wipe your friends on your sleeve.
There is a corolarry
You can pick your friends and you can pick your nose, but you can’t pick your friend’s nose.
As it goes for most truisms, exceptions may be found. You may be able to not only wipe your friends on your sleeve AND pick the nose of your friend (hopefully not simultaneously), but to do either might require some degree of violence (greater or lesser). Unless, your friend(s) voluntarily permit you to perform such disgusting activities relating to nasal discharges of you or them.
In any case, if it happens, then please don’t introduce yourself to me. I don’t wish to know such gross people. Don’t wipe your friends on your sleeve or pick their noses. It’s a matter of courtesy and hygiene, don’t you know?
Thanks for letting me share.