Mine is sackbut.
Heheheh. Sackbut.
Bombardon. Careful how you say it at the airport.
I came in here to say that. Damn.
Theremin. Or calliope.
Sweet potato is a good one.
Tiple. Tee-play!
Composer Harry Partch had some good ones:
Cloud Chamber Bowls
Harmonic Canons
Quadrangularus Reversum
Ukelele (Hawaiian for “jumping flea”) is cute.
Sexophone.
Hurdy Gurdy
Don’t forget the Chromelodeon!
I heard a concert of Partch’s work on his instruments a few months ago. Great stuff!
It’s a toss-up between bratsche and fagott.
Or maybe just violin 
dulcimer
zither.
Rummelpot / rommelpot.
Rackett.
The “Bumba” of course.
Invented by none other than the late Ervin A. Callies (aka “Curley the Bumba King”)
I has never heard of him until he came into a store I was working at in Milwaukee back in 88’. He had a windbreaker on that said “The Bumba King” in big letters on the back. A co-worker said “Hey look, it’s the Bumba King.” I said “What’s a bumba?” He replied “It’s an instrument the use in polka bands.”
“Really?” I asked, “What does it sound like?”
to which my friend answered “Bumba-bumba-bumba!”
Timpani.
To me, it sounds like a tiny, delicate instrument but it’s really great big kettle drums. Go figure.
Well, I came in here to say sackbut, but I guess now that it was said in the first post I’ll say ophicleide instead.
Even though I am no longer interested in playing one, “Stratocaster” is just all kinds of cool as a name…