There's nothing worse than a teacher that can't teach.
Oh come now, really there are lots of things worse.
Degenerative brain disease, sociopaths with assault weapons... the list is nearly endless.
...which means nothing to a person who doesn't know what it is.
Which is why I put it in quotes so that the OP could cut and paste and answer their own question
so i can look them up?
then come back here if there was anything they didn't understand.
(I teach SCUBA diving. All my students have survived, so I consider myself quite good at it)