At 12:08 PM 8/8/1998 PDT, you wrote:

Sigh. Kunou is supposed to be a grand, old samurai nobility type, with 
the flowery poetics and a court dialect. He's a man among men. The 
humour in his character isn't that he acts like a fool (how fanfic 
writers like to portray him, even though he isn't), it's because 
underneath all the fancy talk and eloquent mannerisms, he's just a 
girl-crazy teenager.

He is also either completely unobservant, or is unwilling to deal with the
reality around him.  At one point, while he was embracing onna-Ranma, Nabiki
poured hot water on Ranma, returning Ranma to normal male form.  At that
point, he SHOULD have become curious enough to ask Nabiki, who obviously
knew exactly what was happening, what was going on.

Kuno percieves himself to be a grand old samurai nobility type, but his
behavior indicates otherwise.  He assigned himself the self-agrandizing
nickname of "The Blue Thunder..." in the first episode of Ranma in which he
appears.  [Nabiki's reaction when she hears about this nickname was
essentially "I hadn't heard that nickname before...", and considering that
she seems to know all of the common knowledge of Furinkan, as well as a
number of the secrets, it would be no surprise that she WOULD have known of
a major school personality's nickname or nicknames.  Especially when he is
shown as being in her class.

Try picturing Kunou striking a girl, an old man, or a little child. It's 
simply ludicrous. He would take his own life before he'd let a little 
girl be hurt (although, he'd make sure the word got a big, dramatic last 
speech before he went).

When he set the condition that Akane must be defeated before anyone could
date her, then repeatedly attempted to defeat her, he OFTEN attempted to
strike a girl.  In fact, he incited others to attempt to strike her as well.
In waiting until all of the other guys had attacked her first, he shows
himself dishonorable by using others to attempt to weaken his opponent
before he himself attacked.

As for Kodachi, she is not crazy despite what everyone seems to belive. 

She is extraordinarily obsessive at the very least.  She is obsessed with
her rhythmic gymnastics team winning, enough so that she will ambush future
competitors with the intention of causing sufficient bodily injury that they
are either unwilling or unable to compete.  She refuses to accept that her
pursuit of Ranma is not wanted, deluding herself into believing that he will
be hers.

Obsessive/compulsive behavior is considered symptomatic of insanity,
depending on the degree of such behavior manifested.  

She regularly assaults others either physically or with drugs of various
forms.  [MANGA]

As for Ryouga, he was not so much OOC as he was the victim of a 
traditional character slam. He shows up, screams incoherently, engages 
in indiscriminate destruction leading to the injury of an innocent 
bystander, and then Ranma brushes him aside as he rushes to the rescue, 
which somehow leads to Akane Finding Out About P-chan and beats the crap 
out of him.

Finally somebody that you describe as not being completely OOC!

Given that the character slamming is completely in character with how he
generally shows up after any extended absence [he was training], and will
generally attack Ranma, telling him to prepare to die BEFORE making any
attempt to issue a challenge.  

When he attacks, he is portrayed as generally not caring about collateral
property damage, so long as Ranma dies.

Ranma generally shouldn't be able to casually brush Ryouga aside, but when
an innocent is injured as a result of one of his battles, I could definitely
see Ranma gaining a burst of adrenaline that he hasn't touched for the
battle, as well as a short period of uncharacteristic ruthlessness in
dealing with the source of the injury.   

On the other hand, Ryouga, as an OBVIOUS depressive, on learning that he
injured somebody, should become NEARLY suicidally depressive, and in his
next assault on Ranma, would use the shi-shi-houkodan, blaming Ranma for his
injuring an innocent.

Ryouga always blames Ranma for everything, even when it is obvious that
Ryouga is at least equally at fault.  [EXAMPLE]  He blames Ranma for his
curse, when he should know that if he hadn't been so obsessed with following
Ranma to finish his duel that he would have been nowhere NEAR Jyusenkyo.