Never had any issues with Canadians, Ozzies, Kiwis, or the English. One Irish girl was pretty cool, but was influenced by a USAnian to see the darkseid of the force in anything that went wrong. The USAnian was just young, nothing wrong, just kept seeing things from a Spoon point of view.
Actually, I have never had any issues with USAnian teachers either. Teachers, that is. (except for the minor point that English is English, not American)
However, Nanning is home to the biggest load of retired USAnians seeking young Chinese wives I have ever seen. Many do kind of an elderly backpacker gig with a few paid classes without z visa, interspersed with private lessons and English corners that they get paid for at 100rmb per 2 hours, but I wouldn't call them teachers. They largely live off their pensions in a life of seedy semi-luxury while seeking some poor bint to marry them. Usually they finally end up with some hardfaced slag who has been around the lot a time or two, but they fail to see it, marry (having paid a LOT in all kinds of hong bao for weddings etc, plus 20,000 rmb for the mail order bride guy who ran the website, but usually they don't know that), take them home, get divorced in a year or so once the (ahem) girl get a green card and lose a substantial amount in the process to set the girl up with her new life, then they come back to go around yet one more time.
It is sad but true.
I have also seen one English guy and one Ozzie in this category, but they weren't teachers.
I think these guys should be sent to whatever country they are from by trebuchet. Hell, don't aim, it don't matter what country they are from, or going to. Just load 'em in and cut the rope, spray them across the planet. Do it en mass and save rope. It is doing everyone a favour, including them.