Never loan your vacuum cleaner to anyone.
If someone needs to borrow a vacuum, it means that they have not vacuumed in a very long time and they can no longer stand the crunching noise their carpet makes when trod upon.
If your vacuum is used on such a carpet it will lose half of its suction power and acquire one funky smell. I know because this has happened to me twice before. So the proper thing to do when asked for the loan of your vacuum is to lie.