Update:
It's the day before graduation, and also the day before my roommate must leave the master bedroom and move in to another bedroom (2 roommates were being switched). All 5 people of the house were graduating and thus each had family over to visit. My pranked roommate had his mother sleeping in the same room as him.
Graduation morning - I am in the kitchen when I see my roommate walk in and say, "What the fvck! Who does that...who does that." I immediately start laughing and walk to the his bedroom where I see my other roommate laughing. Apparently as he was laying in his bed, he saw the large picture between the sheet and the wall. Not knowing what it was, he tore down the blue cloth while his mother was walking around the room preparing for the day ahead.
Immediately he realized what had happened and all he could say was "sh!t" while his now skeptical mother looked on. He took down the picture as quickly as possible but not before his mom was exposed to the 4x4 paper monstrosity.
I wish I got it on tape, but alas we could not predict his early discovery of the object. I couldn't even take pictures by the time I knew about his discovery. However, everyone in the house soon knew what had happened, roommates and relatives alike
