Signum delivering a Get a Hold of Yourself, Man! to Teana in the form of a punch that sends her flying back several feet. Signum's response to everyone worrying about Teana being cold-cocked like that:
Signum: "Don't worry, I held back."
Vivio's epic faceplant in Episode 15, immediately after she was told to be careful when running.
Also from Episode 15: Ginga's face after being told she'll be battling Nanoha, Fate, Vita, and Signum. Funnier because it takes a couple of seconds to sink in.
From the same episode again, Mariel's delayed reaction to finding out Vivio's relation to Nanoha and Fate: "Oh, so it's like she's their chi-WHAAA?"
Alto and Lucino Squee! over Reinforce Zwei until she introduces themselves and they react in horror as they learn she's not only cute, but also a few ranks above them.
Episode 12: The villains escaped, and managed to get their hands on the suitcase, and Vita is not happy with the situation. Just as she's giving her report, however, Teana and Subaru reveal that "[they] sort of did something to the relic". Cue the villains arriving back at their base, and finding that all they managed to recover was an empty suitcase. The best part? It turns out Subaru and Teana hid the artifact in Caro's Nice Hat.
A minor bit from the conclusion of the fight between Fate and Scaglietti ans his Numbers: Fate charges at Scaglietti and whams him with the broad side of Bardiche's Zanber Form like with a baseball bat, sending him flying into a wall.
The scene from Episode 13 when Hayate and Fate walk into the room where Nanoha and the forwards are trying to pacify a crying Vivio. Hayate comments rather playfully that "enemies" that the Ace of Aces cannot defeat do exist while Nanoha looks at her friends sheepishly for help.
In one of the earlier battles, Nanoha announces a training match; her vs. the still-fresh Forwards. One of them wonder if they have any chance of victory, to which another of them announces, without hesitation, that they have none.
In Chapter 8 of the Striker(s) manga, Nanoha confides to Hayate that she will have to keep an eye on her Forwards because "they get some really extreme ideas". Hayate's rebuttal of "kind of like you were when you were younger" followed by an image of Nanoha shouting "Maximum Power" with Raising Heart in her hands is very likely to make you laugh a bit.
In the same vein, in Chapter 10 (and Chapter 11 as well) of the Striker(s) manga the Forwards (and most of the Riot Force 6 personnel) try to find out who is the strongest mage in Riot Force 6. Many amusing moments ensue.
After Teana asks Hayate if she could be the strongest one (due to her having the highest rank of "SS") Hayate replies, with a gleeful expression, that she is really weak and would lose to every forward with the exception of Caro, and that is if Caro didn't use her dragons (leaving her with only buffing spells). And then she remembers that Caro got some combat training from Nanoha and worries that Caro too would probably be able to beat her. It's so awkward that Rein II is shown looking defeated and Teana sweat-drops at the revelation (and her face clearly expresses a "what the heck is happening?" feeling)
A bit later Signum is asked who is it that she perceives as the strongest one. Shortly after that Signum remembers (and talks about) a mock battle she had with Nanoha, which she describes as "rather intense". Suffice to say, the one panel of that battle we were shown (with Nanoha trying to fight Signum in melee with Raising Heart as a makeshift spear, both Nanoha and Signum having expressions you'd expect from deranged battle maniacs who want to spill blood) is both disturbing and worth a laugh.
In episode 16, Vita and Zest introduce each other during their battle:
Vita: "Time-Space Administration Bureau's Riot Force Six; Forward Stars' sub commander, Vita."