As per topic, I'm having a real hard time getting rid of these effectively. I'm upto Level 27 and currently doing the Point Lookout DLC, but these guys are just a pain. Im using probably in excess of 20 shotgun shells upclose to the head in VATS, but they just seem to be unbelievably thick skinned.
 
Is there a weapon that's particularly effective? Or a method to get rid of them a bit quicker? Or are they just notoriously tough? These are probably the first enemies that have given me any trouble for a long time, including deathclaws.

...  What level is your regular gun skill? Cuz those guys weren't hard at all for me. Hunting and assault rifles did the trick just fine. Also,  I've noticed that if you're TOO close to people when you shoot them, for some reason you either miss or do like 1/8 regular damage, so maybe take a few steps back?

Pray for a Critical Hit with an Alien weapon. 
 
Other options: Have Fawkes nearby, Mini-Nuke, and/or flee.

 
If you're really having that much of a problem use the fat man or the mirv.

Guns will usually do the trick. But seriously if you still can you should get the Ghoul Mask.

You gotta shoot 'em in the head.

I somehow made the game glitch so even without the mask I never get attacked by ghouls. Pretty weird, but cool.