Guitar

you have no idea how much this hurts me

I think we do.
Such pain

C is for Cello
G is for Guitar
V is for Violin/Viola
U is for Ukelele
Feel free to add on...

A is for Accordion
B is for Bagpipes
Also, B is for Bassoon
C is for Clarinet
D is for Drum
F is for French Horn
H is for Harmonica
Also, H is for Harp
M is for Marimba
O is for Oboe
P is for Piano
R is for Recorder
S is for Saxophone
T is for Triangle
Also, T is for Trumpet
Also, T is for Trombone
Also, T is for Tuba
X is for Xylophone

"a butt tuba" is the same thing backwards

You missed:
E for Electronic Piano
K for Keyboard
L for Lute
W for Wind Chimes

Β is for Bouzouki

sacrilegious!