First off, let's see what the spell description says:
(1st Edition)
"Explanation/Description: This spell enables the cleric to issue a
command of a single word. The command must be uttered in a language
which the spell recipient is able to understand. The individual will
obey to the best of his/her/its ability only so long as the command is
absolutely clear and unequivocal, i.e. "Suicide!" could be a noun, so
the creature would ignore the command. A command to "Die!" would
cause the recipient to fall in a faint or cataleptic state for 1
round, but thereafter the creature would be alive and well. Typical
command words are: back, halt, flee, run, stop, fall,
fly, go, leave, surrender, sleep, rest, etc. Undead are not affected
by a command. Creatures with intelligence of 13 or more, and creatures
with 6 or more hit dice (or experience levels) are entitled to a
saving throw versus magic. (Creatures with 13 or higher intelligence
and 6 hit dice/levels do not get 2 saving throws!) "
(2nd Edition essentially says the same, with a clarification that the
spell will only control the creature for a single round. 3rd Edition
has the addition that it is a "very reasonable command", which would
seem to limit the ability of this spell to the point where your
request becomes unusable).
And just for completionists sake:
exsanguinate
verb (used with object)
1. to drain of blood; make bloodless.
verb (used without object)
2. to bleed to death.
If uninjured, I'd say the creature would be commanded to drain
/something/ of blood by the command, although not necessarily himself.
So I'd watch out, he might come lunging at you with a straw. ;-)
If injured, the command would essentially be the same as "don't
bandage that gushing wound there". It doesn't not necessarily imply
"cut oneself so you bleed". Although I suppose if the creature has
some sort of control of its blood flow it might be compelled to make
its heart pump the stuff out faster, but I can't think of any
creatures with that particular ability.
I think it would only work in the flawless way you assume if the spell
was laid as a trap and only the one character heard it. Unable to turn
his destructive impulses on anyone else, the victim would then turn
his blade upon himself in attempt to fulfil the requirements of the
spell.
Whether he would actually be able to bleed out in a single round is
doubtful given the way D&D handles damage, but I can imagine he might
give himself a really nasty cut that he needs to spend the next round
bandaging.