In 'Harbinger' the look on Trip's face when T'Pol explains that having sex with him was just an 'experiment' on humanity, and the line 'I don't appreciate being compared to lab rat!'
During Reed and Hayes' big fight, a nameless crewman stumbles upon them. Reed orders him, "As you were"—just before Hayes's fist shoots out to send him flying. And the crewman just walks away.
Basically all of "Unexpected", but especially the opening. Archer is in the shower when the grav plating malfunctions and he and the water begin floating upwards. When Malcolm asks if it's caused any inconvience, Archer just casually says 'Oh, no, no, not at all' whilst clinging to the showerhead to stop himself hitting the ceiling. Then a few seconds later they come back online and he falls back to the ground with a weary 'thank you!'
"Perhaps the next step would've been to meet her holographic parents?"
And those Klingons: "I can see my house!"
Trip tries to confirm if T'Pol was trying to be funny.
Trip: Was that... a joke?
T'Pol: Believe me, if I ever decide to make a joke, you'll know it.
Just about all of "Two Days and Two Night", especially Phlox's half-asleep ramblings.
Phlox: I don't care what it tastes like!
I'll bet there's an interesting story behind that comment!
Malcolm and Archer are on a planet with a slightly toxic atmosphere:
In "Shadows of P'Jem", the whole of the scene where Archer and T'Pol are snarking at each other whilst they try to get free of the ropes tying them together. Especially when they fall over and Archer faceplants in T'Pol's boobs.
Just about all of the initial interrogation scene in "Azati Prime," where Archer is really sticking it to the Reptilians.
Archer: Still, the reptiles might've come out on top, if it hadn't been for a slight disadvantage.
Dolim: And what was that?
Archer: They had brains the size of a walnut. That's very small. Apparently, it's a constant in the universe.
Dolim:*visibly resists the urge to strangle Archer*
Trip's reaction to learning about his probable mating bond with T'Pol in "Bound", which makes him immune to Orion pheromones: "I don't know whether to be relieved, or reeeeally worried..."
From "The Forge":
Archer: You had (a sehlat) as a pet?note A sehlat is a large, saber-toothed bearlike creature.
T'Pol: You have Porthos.
Archer:Porthos doesn't try to eat me when I'm late with his dinner!
T'Pol: Vulcan children are never late with their sehlat's dinner.