You do, the nitrogen in your blood expands due to the vacuum of space and causes pretty much every drop of blood in your body to boil instantly.
Then the pressure differential will pull your brain out through your eye sockets.
And the 2 degree Kelvin temperature would instantly cool your boiled blood and cause it to crystalize, effectively shredding every bit of tissue in your being.
FALSE
The human body can briefly survive the hard vacuum of space unprotected, despite contrary depictions in some popular science fiction.
Human flesh expands to about twice its size in such conditions, giving the visual effect of a body builder rather than an overfilled balloon. Consciousness is retained for up to 15 seconds as the effects of oxygen starvation set in. No snap freeze effect occurs because all heat must be lost through thermal radiation or the evaporation of liquids, and the blood does not boil because it remains pressurized within the body.
The greatest danger is in attempting to hold one's breath before exposure, as the subsequent explosive decompression can damage the lungs. These effects have been confirmed through various accidents (including in very high altitude conditions, outer space and training vacuum chambers). Human skin does not need to be protected from vacuum and is gas-tight by itself. Instead it only needs to be mechanically compressed to retain its normal shape.
This can be accomplished with a tight-fitting elastic body suit and a helmet for containing breathing gases, known as a Space activity suit.
