For those many occasions when you have a cold which causes you to have a runny nose and you leave the house in a rush and forget to take a handkerchief and therefore are in need of something to blow your nose.
House bricks - it all depends. Is the house brick connected to a house? The person owning the house may resent you using it to blow your nose.
Domestic pets - with their lush, warm fur, pets seem inviting to the potential nostril in need of an aero-hygenic treatment. However, the adventurous nose-blower should first ask himself a few questions: is the pet awake or asleep, docile or active, etc? Remember: pets have claws, and often bite.
A muffin - only if it tastes bad. And only after you have tasted it to make sure. Don't get confused here: it would be quite awkward if you first blowed your nose on the muffin, and then tasted it to make sure it tasted bad.
Your shirt - are you wearing it to your office? It could still be fine to blow your nose on it - but it is preferable if your office is under a car, or in the mud on a farm somewhere.
Someone else's shirt - generally, the shirts that people are yet to wear are vastly preferable, as they are much cleaner and less likely to smell.
Toilet paper - only before you use it for other purposes. However, be aware that for some curious reason, many sheets of toilet paper these days are lightly scented with floral essences, presumably because people like having floral-scented bottoms. These may make you sneeze.
A book of modernist poetry - Unfortunately, the field of literary criticism is still unsettled in its view on whether it is suitable to blow your nose on this or not. Best confine your nose-blowing efforts to literary productions such as street directories, bus timetables, etc.
A pancake that has been cooked ten minutes ago - Large, pliable, and warm without being hot, a pancake makes an almost ideal surface on which to blow your nose if you don't have a hankderchief. Pity that pancakes taste so nice and you've probably already eaten it by then.
A seat on the tram - it really depends where the tram has been and where it's going. Also, make sure you have a ticket or Myki with you.
Should you blow your nose on this ordinary looking house brick? This is one of the many controversies looked at in today's issue of The Substitute Handkerchief Review.