One early episode features husband & wife arms dealers coming in straight from a gun show where he got shot in the leg. The wife shows off the merchandise... That Came Out Wrong. The wife tries to sell guns in the reception area, letting people handle non-functional samples. Jerry the Receptionist picks up a grenade launcher and speaks of using it on the neighbor's dog who keeps doing his business in Jerry's yard. He puts the grenade launcher to his shoulder and mimes tracking the dog.*
Then he pulls the trigger and fires a grenade into the parking lot, where it blows up an ambulance.
Wife: Damn...I guess Earl used a kit on that one.
In the episode called "Homecoming", Dr. Corday had been having a bad rash all over her hands after a trip to the woods with Dr. Greene. When Dr. Romano asked about her getting exposed to poison ivy, she just looked back at him blankly(being British, she had no idea what it looked like). She asks if it will spread and Benton says that it will spread to other body parts that it has contact with. Elizabeth mutters, "Oh oh", and the next shot is Dr. Green scratching his crotch. But the joke just keeps on giving, Malucci sees him scratching in front of the new med studants and asks him if there's a "problem with the australian boys? You keep scratching down under". Then while Elizabeth is giving him some cream and a shot for the rash, Haleh enters and can barely hold back laughter as she catches them.
A season 7-ish episode involves prankster Dr. Malucci having been hit with a sedative after a prank gone wrong. He remained pretty much passed out the rest of the episode. Another doctor in the meantime was bonding with a very young patient in a nearby room by making and throwing paper airplanes. One unfortunately fwacks Dr. Weaver in the back of the head. She turns around and barks, "Grow up, Malucci!"
In a season two episode, Weaver has set up a camera in a trauma room in order to critique the way personnel handles cases. As she's reviewing the tape for the ER staff, she rewinds it to find an accidentally recorded conversation between Mark and Doug. Earlier in the day, Mark had pulled Doug into the room to confide in him that he was nervous about his upcoming date, the first since his divorce. Thanks to Kerry's fumbling, the entire ER staff gets to hear him confess to Doug that the only person he's ever had sex with is his ex-wife.
"Fathers and Sons": Doug has just told Mark that he's reconciled with Carol. Mark is stunned to hear this (Doug had cheated on her left and right the first time they dated).
Mark: Does she make you take a lie detector test every week or something?
In an early first season episode, a patient comes in with heroin withdrawal and keeps grunting the same note over and over, sounding like a car alarm, while Greene and Lewis work on their write-ups. Hilarity ensues.
To say nothing of the "Peter, I'm pregnant" montage that ensues when Benton is waking up afterward.
Carter is passed out grabbing a nap in an empty exam room. Greene and Lewis, being two of the more mature members of the staff, busy themselves with putting his leg in a cast. Then they have the receptionist page him, leading to Carter stumbling groggily into the hallway before losing his balance and falling on his face.
Later in the same episode, a scary-looking biker who had brought his wife into the ER proceeds to grab a saw and cut the cast off for Carter, much to Carter's dismay.
Carter is bringing a patient in while Benton grills him on various medical details of the patient before asking, in the same demanding tone of voice, for the patient's mother's maiden name. Carter frantically flips back and forth through the patient's chart before nurse Haleh informs him that the last bit was a joke.