The "Can you hold the door for me? I don't have my key/access card on me." one is particularly serious problem for a large workplace. An another version would be "Can you hold the door for me?" while carrying a box of "paper for a printer" using both hands. Without other additional security measures, an unauthorised entry is only a matter of time.

Another sweet one I read about was this one. They stuck fake parking tickets on people's cars. On the ticket it said "If you don't agree with this ticket, you can file a complaint here ...." etc. The URL was something like police.parkingtickets.com: something which did not raise immediate alarm bells.

People got pissed because of the ticket and took immediate action. When people went there, they got a popup box, saying "Your Flash player needs to be updated for this site to work" After "yes" the damage was done.