Now he does, and he's proud of it. To prove his love, Monahan took to YouTube last April and created the first of three videos to promote the glory of the Philadelphia (that's Phulluhphya to you) accent.
Linguistically, Philadelphians speak in a mid-Atlantic dialect, according to the Atlas of North American English, developed by University of Pennsylvania linguists, including William Labov, who has studied the Philadelphia dialect since 1971.
But we have our own way of speaking that differs from someone who grew up in Brooklyn, Baltimore or Boston.
Most people don't really know what the Philadelphia accent sounds like, Monahan noted, and that was one of his inspirations for making the vids. Boston, Chicago and New York are easy to pick out, but our accent is a little more subtle.
As a primer for the criminally uninformed, Monahan's first video, "Phulluhphyin Dolleck," explains the accent in great detail, complete with phonetic subtitles. ("Heaw youse dewin dudday? C'I getcha sum da drink, hun?" Translation: "How are you doing today? Can I get you something to drink, hon?") It's gotten more than 12,000 hits.
One of the reasons the Philadelphia dialect isn't widely known is that it's often portrayed incorrectly in the media, Monahan noted. When a movie or TV show is set locally, actors typically fall back on a New York City accent.
In his second video, "Da Philly Accent inna Media," Monahan chastises bit players in the Philly-set movie "Invincible" for faking their way through it. Rocky Balboa himself didn't even get it right.
Monahan uses clips from "Jackass" Bam Margera and political pundit Chris Matthews to illustrate the correct way to rock the Philly accent.
The third video, "Vurry Murry Chrissmiss," is more parody than education. It features Monahan singing Christmas carols in a comically exaggerated accent. "All produced in the nasal accent you love!" he says in the video.
Labov, directed to the videos by a reporter, was impressed with Monahan's amateur work.
"Sean is a phenomenon: He's identified almost all of the sound changes that make up the Philadelphia dialect - which, as he knows, is very similar to Wilmington and Baltimore," Labov said via e-mail. The professor also found some of Monahan's phonetic spellings intriguing.
"I was particularly struck that Sean uses the pronunciation that he spells 'uy' not only to 'night' and 'white,' - words ending in voiceless 'p, t, k, s' - but also to 'spuyder,'" Labov said. One of Labov's students noticed similar patterns in his own speech and research.
Monahan said he's always been interested in accents - British, Australian, Irish - but never formally studied them. When he's not making videos, Monahan works at a nonprofit that helps low-income people with their taxes, a job he got through AmeriCorps. He said that one of his favorite things to do during conference calls at work is to guess where the various speakers are from.
But it's his hometown accent that he loves the most.
"A lot of people think it sounds ugly, and people don't say that about New York, Boston or Chicago," he said. "And I don't like that - I like the way it sounds. Sure, it doesn't sound refined at all, but it's part of who the city is, and people should be more proud of that."