It is rude to wipe your nose on your clothes.
Little Reilly has a cold and his nose is running a lot.
Reilly wants to wipe his nose.
Reilly gets a tissue to blow his nose into, then throws it away.
Reilly wipes his nose on his shirt, getting his snot all over it.
Reilly's nose is less runny and no one is grossed out.
Reilly is scolded by his mother and has to change his shirt.