SPOILERS: Don't think it, don't say it, don't watch it. I was forced by IMDb's regulations to give this one when I wanted to give it zero. Now, I know there are a great many reviews on here that blather on about what was so awful about this garbage film so I won't go into unnecessary detail.
So what did I find so horrid about the Bye Bye Man? In short, everything. The acting was terrible, the writing was bad, the story wasn't thought through, and, most importantly, the bad guy's backstory was not explained at all (thus leaving the audience confused in addition to angry that they wasted their money.) Even the movie's editing was choppy and jarring. There is not a single redeemable feature to this movie and trust me, I wanted to find one.
The Bye Bye Man? Should have been called the Shouldn't Have Been Made Man.