can't make heads or tails of

can't make heads or tails (out) of (someone or something)

Cannot understand someone or something at all; cannot make any sense of someone or something. I've been working with the new software for hours, but I still can't make heads or tails out of it. I can't make heads or tails of that new guy in accounting. Sometimes, he's really friendly, and then other times he acts like he's never met me before.
See also: head, make, of, tail
Farlex Dictionary of Idioms.

can't make heads or tails (out) of someone or something

Fig. [to be] unable to understand someone or something. (Also with cannot.) John is so strange. I can't make heads or tails of him. Do this report again. I can't make heads or tails out of it.
See also: head, make, of, tail
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • cannot make head or tail of something
  • can't make head nor tail of (someone or something)
  • can't make head or tail of
  • can't make head or/nor tail of something
  • can't make heads or tails (out) of (someone or something)
  • I can't even
  • can't even
  • cannot
  • cannot but
  • (Are) you kidding (me)?