Leah's extremely painful looking Groin Attack when Loki tries to turn some charm on her the first time they meet.
The Running Gag of Journey into Mystery #624-625 involves Kid!Loki getting progressively worse news and reporting it to Hela/Mephisto:
Loki:[end of #624] Dire news!
Loki:[start of #625] Dire-er news!
Loki:[after a momentous discovery towards the end] Dire-est news!
And by the end of it, Hela's handmaiden Leah looks ready to smack him.
Loki acting like he's still the evil bastard Hela and Mephisto remember him as (and capitalizing on that reputation against the Tongue of the Serpent) and then turning right around and gleefully lampshading it to his companions once the coast is clear.
Loki: "More to fear than me"! Oh Tyr, how fun this villainous talk is! (issue 625)
Loki: And the Tongue will give it to us, or we'll tear it out at its bloody root. *turns to Ikol, his magpie familiar* That's the sort of thing I'm meant to say, yes? (issue 624)
Also in issue 622, where Thor comments that Loki isn't as bad as people think he is, and Loki indignantly comments:
Loki: I'd have to try terribly hard to be that terrible.
Kid!Loki discovers the internet (Issue 622)
Loki: When I said I was an Asgardian god, they called me a troll!
Loki: I want to learn. If Midgard is to become our home, I would know of it. I've primarily discovered that mortals like to rut, and chronicle the experience pictorially.
Thor: I'm not sure I approve of this eith—
Loki: How do you know about Stark phones?
Most of 632, which is Loki trying to find homes for seven hell-puppies at Christmas, complete with Loki's attempt at giving Leah a Christmas present, and the introduction of Thori, the bad-tempered foul-mouthed hell-puppy.
Tyr, with Thori chewing on his good wrist:Not again!
Thor: They have hammers, Volstagg. I have the hammer. That's my thing.
The Terrorism Myth arc starts with Loki and Leah in a fast food restaurant where Loki is introducing her to milkshakes. She ends up throwing a man out the window during an argument. After the whole arc, Kid Loki takes Leah back there to apologize, maybe thinking he'll have to pay for a soda for the guy, since Loki already had to shell out to fix the window. Leah decides an apology is not enough, and throws herself out the new window, meaning Loki has to buy another one.
Loki:[still deadpan] I could have many reasons to amble into your maw. It could be jealousy of my brother. It could be desire for one-eye's throne. It could be the terrible lust I hold for older men with crazily serpentine tongues.
While it's not something that's likely to be noticed right away, Kid Loki's habit of greeting possibly dangerous people and creatures with a cheerful "Hello, [name]!" becomes really damn funny after a while.
Loki and Leah's insistence on making jokes at the other's expense during the destruction of Dark Asgard - one of their jokes even has a beat panel of them just laughing over it:
Loki: And Leah...
Leah: Prepare a portal to a place other than here?
Issue #652: Sif misunderstands the term "walk-in clinic".
Sif: I think that woman drove to the walk-in clinic.
Sif and Jane crack puns at Thor's expense.
Sif: I have never talked to a vegetable in my life. Jane:[simultaneously with Sif] Except for Thor.
Sif: He can be a little starchy. Jane: Surprisingly green sometimes.
Sif: He is bold, but you and I in the same room would scare him half to death. And rightly so.
Issue #654: Something or someone planted Skuttlebutt, Beta Ray Bill's ship AI, into the body of Bill's recently dead girlfriend. Bill is quick to roll with it after Skuttlebutt proves himself, but Sif needs convincing.
Sif: You were dead! Beta Ray Bill: It's Skuttlebutt!