Some audience members came prepared with full-body rainsuits and sheets of plastic, which largely proved ineffective against Gallagher's relentless projectile assaults.
Others weren't afraid of a little goo. "I want to be submerged," said Jeff LaSorsa of Greencastle.
"I don't want to wear a poncho," said Michelle Scholtes of Frederick, Md., who just turned 10. "I want to get messy."
"We ate before we came but we'll snack while we're here," said Scott Fredricksen of Germantown, Md., who brought a roll of thick plastic. "I guarantee we'll come out chewing."
That was precisely the advice Gallagher gave. "If something hits your mouth while it's open in amazement, just chew it down," he said.
"I've seen every video," said Jo Dunnavant, of Hagerstown, who came prepared. "He's my hero." Dunnavant said she liked Gallagher because he was a regular guy and didn't have an obnoxious edge like some comedians. She received tickets to the show as a birthday present, she said.
"This rounds out my three wishes. I'm tickled. I specifically asked for seats in the splash zone."
Dunnavant commented on some who came without protection. "They're in for a surprise, especially when the dog food starts flying."
When audience members reacted to a little water splash, Gallagher chided them. "Ah, shut up and sit down. What did you think was going to happen in the front row of a Gallagher show?"
He got few laughs with his one Hagerstown joke. "Is this a town? Well it's a pretty haggard town."
One kid stuck his tongue out at Gallagher and received immediate mustard spray retribution.
"Who else wants to stick out your tongue at me? I've got enough mustard for everybody."
Gallagher also said God wasn't a woman.
"If God was a woman he would have never made dirt. She would have made carpet."
"Women don't want to be logical, they want to be mysterious. Women shave off their eyebrows and then paint them back on - for what?"
When some kids grew impatient and urged Gallagher to "mash some stuff," he told them that it wasn't that simple - one had to scientifically look at how to maximize the projectile power.
"You see, preparation is the whole thing. You don't just go smashing groceries."
LaSorsa said he loved Pauly Shore's show in Hagerstown earlier this year and said he wished more acts that young people could enjoy were brought to the area.
"Basically, any good entertainment in this area is hard to find," LaSorsa said.
"It's good clean fun," he said.
Gallagher will perform at the theater again tonight. The show is sold out.