There's one in the corner of every staffroom of every school. The chap with the dully glazed grey watery eyes, the slack expression, the clothes dusted with chalk, although we stopped using chalk in '93. The man the job defeated long ago.

He's the bad smell in the staffroom who tails a conversation about the room hopefully, unable to join in. The dreaded bon vivant who flounders and fumbles until even the nicest staff assume a glazed stare, slightly to the left.
He's the one who survives forty minutes plus of glazed stare, slightly to the left, before taking a hint and bumbling stage right.
It's more than mere annoyance-reluctance-boredom on the petulant listener's part - it's at least in part a strong, natively instinctual superstition.
He's a broken ladder. A black cat, a spilt salt cellar.
A broken mirror which potentially reflects us all.
This man is a pedagogical Ancient Mariner. It's seven years bad luck to be trapped by his tale of woe.

He's the Permanent Cover Teacher, the supply staff for nearly thirty years. He's the teacher whose sheer volume of indiscipline creates more problems per minute than you can believe, the one you can't help out, as the senior manglement stopped responding to his distress calls ten years back on principle.
Along the school corridor, you spy him by his lumbering gait, the galumphing stride when aroused to fury, the alternating between gruffly impenetrable meandering mumble and ineffectual roar, more volume than content.
The one with no marking, no planning, no reports to write, and no responsibility or status. Moved onto the supply roster fifteen years ago in desperate attempts to find something to do with him, somewhere to go. Something, anything, to put him beyond disaster's reach.

He's the one, in fact, who put in thirty full, hard years in an inner city school, and lost his mind.
He's not pretty. But he will get his carriage clock soon.