That one crap gun in Borderlands 2 for example. If you don't know what it is, youtube it, it's pretty interesting.
Stapler, It makes a clicking sound you attack with it and it shoots a staple like 2 blocks in front of you for 1 damage. FEAR ME *click* *click* *click* *click* *click* ...Crap I'm out of staples.
I'm sorry but- jUst Yes please I fucking LOVE Joke weapons, ESPECIALLY if you take the time to power them up they become one hit kill machines. Oh Paper Airplane from Castlevania: SoR, 5 shotting Dracula...
Pop corn gun you see the corn popping in the back and it goes out the front mobs maybe birds hop around eating it off the ground.
Super Robots = WIN. I was more referring to your SD format avatar. I'd like to whack some people over the head with it. But yes, I see your point. Edit: And while I'm on the topic of Super Robots...ROCKET PUNCH.
What about deadly pillows? Your mate would think that you're running towards her with a soft pillow, when it's actually filled with bricks? Or if you feel extra evil, fill it with pieces of glass? Gentleman's glove, Let your inner fury out, like a Sir! Beehive, throw it on someone and watch them run to the hills. That's about all I had, I would never suggest this under anything else than just '"Joke" Weapons'.