(adj) When a person, group, or other collective makes a decision(s) or commit action(s) that present problems for them and/or others which would tend to make an unbiased third party observer believe the perpetrator(s) is(are) mentally unstable.
"Joann's tendency to throw up after she eats is very problemental."
"Stevo has been so problemental lately; his irrational behaviors are quite disconcerting."
"The NRA's defense of guns after the SandyHawk Massacre is very problemental."
Someone who jumps from one relationship immediately into another one.
Serial monogamists can not stand to be alone and often suffer from vast commitment and insecurity issues.
Because they jump into relationships immediately after the previous one has ended, serial monogamists typically don't take the time to reflect on their behavior or why their previous relationships failed; thus, they end up making the same relationship mistakes over and over again.
Person 1: Damn, Dustin already has a new girlfriend?! It's only been two weeks since he broke up with his fiance! I think he's a sociopath.