Jinnai's behavior in general, thanks to his status as a Large Ham, but especially this one line from the first OVA, when Ifurita is ignoring him:
"They don't make demon gods like they used to!"
One simple one, by Ura. Makoto is fiddling around with some strange Roshtarian technology while idly talking to Ura. As an armor cat, Ura is capable of shrugging off a lot of damage. Ura still has this to say about the experiments: Makoto experiment scary. What makes it so funny is the nervous-but-deadpan voice it's delivered in.
The Big Lipped Alligator Moment mentioned on the main page is funny already for the sheer "what the fuck!?" factor of it, but Fujisawa's comment to Makoto really clinches it: "You saw that too? I thought I had the DT's!"