I think, therefore I yam.
OOOOO! Existentialism!
Where’s Voltare when you need him? 
To echo some other posts, I get bills in the mail, therefore I must be real!
Also:
Cogito Ergo Vroom! I think, therefore I drive fast.
(I think this was someone’s sig once)
How many absolute solipsists does it take to screw in a lightbulb?
All of them.
Define “exist,” and I’ll tell you whether or not I’m doing it.
Until then, the answer is “I might.”