That usually happens when I'm not wearing my glasses. Unfortunately, I usually end up apologizing to the wall, except I usually say "Sorry, sir" or "Excuse me, ma'am". Created quite a stir back in 1980 when I went through the hall where the hearing-impaired students had their homerooms (some of them still tease me about that day, even today, but I get them by showing them what my world looks like without my glasses by having them look through them [as long as we're sitting].).
Now, I try to get two pairs of glasses and keep the spare pair aroung just in case.
Phyllis (aka Sidhe Uaine or Gaia Euphoria) i.e. your fellow bruised poster