Lindsay Lohan -- The Happiest Prisoner EVER!!!

5/26/2011 5:12 PM PDT
You are looking at Lindsay Lohan serving HARD TIME under house arrest at her swanky townhouse by the beach ... OH, THE HUMANITY!!!

During her first day in confinement, Lohan entertained a mystery guest ... with a big, fat smile on her face.

As we previously reported, Lohan is expected to be under arrest for roughly 35 days. How will she survive?!!?!?

UPDATE: The woman in the photo works with the company that makes the electronic monitoring device and was there to give LiLo an orientation.