A/N- I was looking around my kitchen and this popped into my head. V. short, but oh well.
"Stay back I tell you! I'm armed!" The Doctor brandished the sonic screwdriver in what he obviously thought was a gun like fashion.
"Don't try and kid us." The tentacles aliens voice dripped with sarcasm.
"I mean it! This SS-360 could blow all of you up in a matter of moments!" The blatant lie was apparent in the Doctors voice. In a moment of desperation, Donna slipped out of the aliens grasp with ease and went to join the Doctor before anyone noticed. She riffled through his pockets from behind, looking for anything useful. She came across something that was very suspiciously shaped like a deformed gun, so she pulled it out and aimed at the fleet of green tentacles aliens with as much sincerity that she could muster.
"We're not kidding. Back away now, or the Emperor one gets it."
She pointed the supposed gun at the one wearing the crown, who stood out like a sore thumb because no one would stand within two feet of him for fear of having their heads chopped off. They all gasped in synchrony, and backed away from them slowly. After Donna sneaked her finger round the front of the thing in her hands, they knew she meant business and ran for their lives. The pair heaved a big sigh of relief, and collapsed into fits of laughter.
"Why in the name of all things TARDIS do you keep a banana in your pocket?" Donna asked.
"Don't underestimate the power of a banana. Great source of potassium, keep you going till lunchtime and there also rather good at imitating a highly powerful gun."
A/N- I love bananas. Aren't they just great? Please tell me what you think!