I cant believe some of the names guys are tossing out, alot of them are guys who have survived some monster shots, they just got caught eventually. However Goulet, does seem to get rattled by less than flush shots.
A guy who I think should be mentioned is Marvin Eastman. Main reason I mention him, is he got 1 shot KO'd by Lutter, and though it was a nice punch........
Sakara I think may need a mention too, he gets rattled pretty easy for a guy who is supposed to be such a standing killer.
bhealthy - Jay leno
With regards to Arlovski getting Ko'd by 'bombs'.. I would argue the Fedor punch was not that hard of a punch compared to other Fedor punches (Rogers ko or the famous Shots big Nog took for example). Arlovski's weakness is his chin. 
Whoever said Terry Martin...Belfort, Smith, Leben, Irvin...all vicious KO's
I always hated chuck liddel's fighting style, and don't think much of him as a person, but he had a granite chin for years,
He got old, thats what happened....period.
Jardine
superCalo - Goulets chin is not that bad, he took a couple of good shots from Marcus Davis before Marcus knocked him out.
I'm sorry, but while Jonathan Goulet was a very talented MMA fighter he did have
a pretty bad chin. He was either rocked or knocked out in almost all of his UFC
fights and he had seven (T)KOs in the first round. I really do believe that if he had
had a better chin Goulet could very well have been a top tier MMA fighter and at
the very least wouldn't be 23-12.
I'm actually kind of surprised no one's mentioned Kendall Grove so far.
Andrei Glassjawski, and I've always been a big fan, but his chin is his kryptonite, always has been.
Arvloski, no question. The thing is he is good enough to fight top notch fighters and win but his chin gets in the way :)
The Mail Man - Rashad Evans and Liddell.
0% chance the above post is serious
"LMAO at people saying Arlovski, the shots that put him out were absolute killshots."
Yeah but youre forgetting the tendency of morons to repeat what they hear.
Arlovski was put out by Rizzo, Sylvia, Fedor, and Rogers(going all the way back, Datsik). All of them are devastating strikers. Ricco just kind of beat the crap out of him until it was stopped.
The shots that put him out, with the exception of Sylvia which while not huge was totally out of nowhere and Andrei ran right into it) were all bombs.
Saying Arlovski has a bad chin really says "Ive never trained seriously in my life and have no idea wtf Im talking about"
A bad chin = a guy who gets dropped or finished by strikes that shouldnt be fight enders for that weight class or by guys who are not known to KO anyone.
Rizzo is truly a sad story, like Mino. had the best chins in MMA & now get knocked out on the reg. the noobs will never know the history
"His UFC record was 4-5, with notable wins coming against Jay Hieron and Luke Cummo inside the Octagon."
How did Goulet beat Hieron!? Dont recall that one....
lesforpres - The problem with arlovski is that he wasnt a big enough heavyweight to really have a strong chin, and he didnt have a gigantic head like brock or shane, so he had more of a lightheavyweight chin.
Sheesh.
HELWIG - "His UFC record was 4-5, with notable wins coming against Jay Hieron and Luke Cummo inside the Octagon."
How did Goulet beat Hieron!? Dont recall that one....
It's the fight that the UFC didn't air and you have to search for...Goulet blew up Hieron's face.
Right now Liddell
AA has been KOed less than the Reem.
jjj2121 - LMAO at people saying Arlovski, the shots that put him out were absolute killshots.
Right. People throw AA's name out there because he was knocked silly in a few high profile fights. You could say his defense is suspect, not necessarily his chin. The Fedor shot in particular no one would have survived, and anyone the size Sylvia that solidly lands an uppercut will drop you.
Goulet is the highest profile fighter I can think of.
"The problem with arlovski is that he wasnt a big enough heavyweight to really have a strong chin,"
Really. Andrei was 6'4 and 245lbs of lean muscle.