The act of doing something personal for the benefit of other people that in fact benefits the individual doing the action. For example, a person may brush his teeth in the morning so his breath won't smell bad, but benefit personally from having clean teeth. Simillarly, one might organize her office to appear organized to co-workers, but benefit from the organization.
Origin: Personal Information Management (PIM) 2009 Workshop, Vacouver, WA.
Fred's dentist appreciated the toothbrush effect, both because Fred's teeth were cleaner, and because Fred's breath smelled better.