When you're reading and you can't get comfortable so you're like:

Criss-cross applesauce:
Aah! My neck! Ow, ow, ow.

On your back:
Arms. Hurt.  Crap falling into my eyes.

On your stomach:
Mm phs mph m mphrble mph it mphmph hmph.
Translation
Well this would be comfortable if it didn't hurt.

Leaning back in a comfortable chair:
Ah. Now if only I could see down and rest my head back at the same time.

Underwater:
Can't. Breathe.

In a tree:
Ah. Aaaaaaaaaaah! Snap! Oh snap.

Upside down:
This could be very nice, but right now, the extensive amount of blood rushing to my head isn't really helping.

Piled on top of your friend(s):
Perfect.