It was common knowledge in S.H.I.E.L.D. bases to avoid air vents and ceiling tiles whenever a certain assassin visited. He was especially bothersome when his best friend joined him in his antics; a week at the training academy was better than being caught unexpectedly by the two. Rookies, who were unaware of the assassins' vicious attacks, often wandered into shooting range. The rookies would be found several hours later, covered in nerf bullets, tied upside down in a room with duck tape over their mouths, usually unconscious. They pair got away with it, mostly because they avoided cameras, and because Coulson went easy on them (who wouldn't? Rookies, to most older agents, are the most annoying thing in the world, and can be down right mean, not to mention rude). Most who survive say all they saw was a flash of red, nerf bullets raining down upon them, and then the world upside down.
Natasha and Clint loved terrorizing new agents; it was their favorite past time. They seldomly attacked older agents because they avoided their hiding spots, and because they were more likely to retaliate. The two assassins would lie in wait in air vents or ceiling tiles, awaiting unsuspecting prey to wander into their firing zone. While they waited for their perfect target, they caught each other up; they would tell each other about their current missions, discuss the latest briefing, or complain about Tony Stark. After they fulfilled their game of attacking agents, they would return to their rooms, awaiting the accusations sure to come.
Sure enough, a few hours after the rookie agent or agents were found, Coulson would come barging into whoever's room the two were currently occupying, spiting mad, lecturing on and on about not harming people for fun, that it was a bad thing to terrorize new agents, that he raised them better than that; the two never listened. They'd heard the speech if not once, then a thousand times. Even Coulson sometimes just glared at them instead of speaking because they could practically read his thoughts on the matter. Most of the time though, after all of Coulson's steam evaporated, Coulson too would have to forcibly hide his smile as the assassins' explained to him exactly how they had captured their latest prey.