Connor's explanation to the police of how a decapitated man ended up in an underground carpark.
"This Fasil was so upset about the lousy wrestling tonight, that he went down to the garage and in a fit of depression cut off his own head!"
This set of jabs at Lieutenant Moran from Tony the Hotdog Vendor:
Tony: [as he reads a newspaper headlined: Headhunter-3, Cops-Zero] Hey Moran! Have you read what it says in here?
Moran: You kiddin' Tony? You know cops can't read.
Tony: [Teasingly to Moran] What does "incompetent" mean?
Moran: [Speaking to Detective Bedsoe] That mayor, he calls me at 2 o'clock in the morning! I mean I don't even answer the phone anymore!
Tony: Hey! What does "baffled" mean? Hee hee hee hee! Ha ha ha ha!
[Moran and Bledsoe give Tony an irritated look]
The Kurgan. He's evil, but he's also funny, so you're laughing right along with him as he does all this evil shit with pure glee. And you feel kind of bad afterwards.
While enjoying some down time on holy ground, the Kurgan teases some nuns and makes snarky comments to the church's priest.
The Kurgan: Forgive me Father! I am a worm!
The Kurgan rips the roof off an old couple's car with his sword, then throws the old man out of the car with one hand. He then gets in the car, and utters "MOM!" then "WOOF!", scaring the crap out of the old woman, and starts driving like crazy.
The "Duel on Boston Common", from start to finish. To elaborate, Connor turns up drunk off his ass, unable to even turn to his opponent. Bassett proceeds to stab Connor repeatedly, who is pretty much oblivious to the whole affair. Bassett gets so frustrated that he kills his servant.
The Mood Whiplash felt when the love scene between Connor and Brenda is suddenly interrupted by a roaring lion at the zoo is such that if you're not startled by it you're probably chuckling instead.
Sean Connery finds haggis revolting. On a meta level, that is bloody hilarious.
The entirety of the episode "Double Eagle," with Duncan trying to keep his friends Kit and Amanda from killing each other (and flashbacks showing how the rivalry started). Highlights include:
Kit sneezes when he feels the presence of another Immortal. At one point, he senses Duncan and Richie together. . . and sneezes twice.
Duncan lies to Amanda to try and keep her and Kit away from each other. Amanda know Duncan's lying, but thinks he's seeing another woman. To make matters worse, he ducks Amanda by leaving her with Richie. She uses seductive fast-talk to figure out Duncan's as the race track. When Richie catches up, all he offers for explanation is "It was Amanda. I never stood a chance." Duncan just nods like "Yeah, I should have seen that coming."
Amanda telling Kit she threw his lucky Double Eagle gold coin into the sewer. Note they're about two seconds from fatally crossing blades in the main room of Duncan's dojo.
Amanda: Some rat's got it and he's probably winning. Richie: (laughs) Duncan and Kit: (Death Glare)
The fact that the whole thing boils down to one big misunderstanding. Kit lost his Double Eagle saloon to Amanda in a game of poker (she was hustling him, and Duncan tried to warn him). Kit called in every debt, favor, and marker he was owed to get together the money to buy it back, but Amanda wouldn't sell. Kit tried to claim his lucky Double Eagle coin, but Amanda insisted it belonged to her, like everything else in the saloon (mostly because Kit was drunk at the time and Amanda didn't like his attitude). Duncan convinced her to give the coin back. . . then the saloon burned down. Convinced Kit had done it to get back at her, Amanda threw the coin in the sewer. Duncan had to prove that Kit wasn't responsible (because he was on a ship that sank at the time), as well as convince Kit that his losing streak was over, so revenge on Amanda was no longer important.
"The Stone of Scone", a Whole Episode Flashback and another comedy episode, with Adrian Paul, Roger Daltrey, and Elizabeth Gracen clearly just having a ball. It starts with a Historical In-Joke of Duncan MacLeod and Hugh Fitzcairn meeting in the tunnels under Parliament. Duncan's there to steal the Stone of Scone (pronounced "Scoon" in the episode), historically the throne of the rightful king of Scotland (placed under the throne of the King of England to make them the rightful king of Scotland as well). Fitz is there to blow up Parliament with a wagon of gunpowder. Hilarity Ensues as they fumble each other's plans, then meet on the field the following day to settle their differences. . . over a game of golf. Winner helps the loser with their plot (Hugh cheats). They still can't pull it off. Flash forward to the 1950s, and another golf game, this time with Amanda tagging along. Fitz tries to cheat again the exact same way he did before, but Amanda catches him, leading Duncan to realize that he should have won all those years ago, and now calls in Hugh's assistance to steal the Stone. Amanda, thinking something impressively named "The Stone of Scone," and Duncan considering so important, must be an impressive and expensive gem, wants in on the heist to pay off her debts. More comedic errors ensue, resulting in Duncan replacing a fake stone that he accidentally cracked in half while making it (another Historical In-Joke, see That Other Wiki link for details). The real stone is sitting at the golf course where all this silliness started, two little old Scottish ladies using it as a bench. And as Amanda points out, whoever sits on the Stone is the rightful king of Scotland. . .