Yeah, Tactician secondary badge is stupidly difficult, I guess to make up for how balls-easy the spawn point badge is. Engineer is the opposite, the first bot badge is hard--though not nearly as hard as airbots--and then repair seems like a breeze (not sure, since I don't have it, but it sure looks it).
Probably the hardest single badge has to be the melee specialist one, though. When I throw two airbots I usually get a few kills out of them, even if five is tough. Ten melee kills in a single game, when enemy guns are so rapidly fatal as you run up, and melee is so hard to aim? Insanely unlikely without farming. I've never gotten a single ribbon, even in a couple melee-only matches I played! (Since you always have a pistol with rounds, lots of folks love to shoot in those games anyway.) Or perhaps I'm just lousy at it.