A corruption of the word Haole, Hawaiian slang for foreigner. Usually applied only to Caucasian people. Not necessarily derogatory, depends on context.
If you look up Haole on urban dictionary and spell it Howlie, you are probably a Haole.
Specifically used when a woman doesn't like to swallow - after a man shoots his load into a woman's mouth, he immediately pulls out and pinches her nipple, causing her to howl in pain as she gargles on the cum – sounding like Chewbacca
Disappointed with the fact that his new woman doesn't swallow, Mark decided to top off the blowjob with a Chewbaccan Howler.