Hrm... I can say I've seen my share of this in the past.
I view it as more of a under-developed character, particularly the ones like you described. Sure, they romanticize and almost glorify the horrific past of their characters, saying they're big and bad, but as you said, it falls apart when they actually go to roleplay it. They just don't stick with the personality they envisioned for the character, often because the Rp wasn't going the way they'd planned.
It does get a little frustrating when some floofs get out here and don't really play their own character's part, but I guess all of that comes with experience. c:>
Although, if I were in that warrior Rp you described, I probably would've prompted the 'big bad kitty gone soft' by having my cat say something like this:
"Where's your dignity?" The she-cat rumbled, unimpressed by the loner's sudden groveling countenance. "You came in here like you didn't care of you started a fight; Why so quick to make friends, now?"
Like that. Probably. XD It might prompt them to stick to their character's personality. But, if not... Eh. -Shrug- Derps will derp, then.