'Spontaneously Combusting fleet members?'
I am pretty sure, though do not quote me on it, that in one of unreleased episodes of the original series (TOS, all rights reserved), McCoy actually does. It was during one of his famous arguments with that damn Vulcan.
McCoy : Logic? The man is dying, Spock!
Spock : Yes, doctor. It is... unfortunate.
McCoy : 'Unfortunate'? 'Unfortunate'?? Why you inhuman, green blooded....
*muffled flash, followed by a searing flame... not even the eye shadow could save the man*
Spock : Fascinating.
*off camera* Uhura : I think I'm going to be sick, Captain.
Kirk : My... God, Spock... Bones? He...
*Spock scans the debris with a tricorder. Satisfied by its readings, he bends down and sifts through the remains. He stands, and displays his find to the bridge - it appears to be a femur.*
Spock : Yes, Jim. I believe the doctor... spontaneously combusted.
*Chekov gingerly touches Spock's find*
Chekov : Vell, Kaptain... at least the docktors neekname served him vell till de end.
*Crew stops their movements, staring at the young Russian for a moment. They suddenly break into gales of laughter. Segue to credits.*