I agree that its entirely up to you on what behavior to terminate. I once terminated an infant who just cried it seemed all day. it wasn't really like a "behavior" issue. nothing i could really write on a termination slip but it was an issue enough for me and my sanity that they had to go. Id talked to mom about the crying for a little over a month on an almost daily basis so when it came to termination she wasn't upset or surprised, id like to think she respected me enough for trying with her child that long. (she wasn't always so unhappy it seemed she just got real colicy and i had 5 other kids, 2 babies to care for so it wasn't gonna happen)
Its not easy but if its to the point to where its them or your sanity choose you and your sanity
thats just what id do. i have to be the best i can for my family, and the ones i care for.