If you can’t “make heads or tails” of something, it means you’re confused and can’t figure out what to do. The phrase may have been born in Ancient Rome, in a phrase used by Cicero, (106 to 43 BCE), ne caput nec pedes, which means “neither head nor feet.” In other words, you can’t tell which end is which.
Sometimes we make a choice by flipping a coin, because either outcome, heads or tails, has a likelihood of exactly 50 percent. “Heads” refers to the side of the coin with a human head on it. “Tails” refers to the opposite side, merely because it is the opposite. Sometimes there isn’t a human head etched on the coin, so you can’t tell which is heads and which is tails. In that case, you can’t make head nor tails of it, right?
All this could mean you’re “out to lunch.”
If you’re “out to lunch” you’re inattentive, absent-minded, not in touch with reality, stupid, crazy, or not all there. Your mind took a lunch break and never came back.
The expression is modern. It originated on American college campuses in the 1950s and first appeared in print in 1955.
Then again, perhaps these quick definitions apply:
Pea brain — stupid person
Nutty as a fruitcake — crazy, idiotic
I have to stop this before I go entirely squirrelly.