Dear Mr. Tenor,
I need to express my deep concern about the last few weeks of church choir practice I've had to endure with you.
First of all, I'd like to remind you that singing in the church choir is a voluntary commitment.  No one is forcing you to be there.
Second of all, remember at the first practice -- the first of only four total practices, our worship director asked that we commit to this, making sure to come to each of the scheduled practices for Easter service?  Well, this point isn't actually directed at you because you have been at all four practices.  Not exactly happy to be there, but still, you were there, so I guess you committed yourself.  Thanks for that.  No, this point is more directed at the 8 other people who came to the first practice and haven't shown up since.  Until tonight, the final practice, and wanted to know what they had missed the past two weeks.
Third of all, it's a choir practice.  We all sing different parts, which is needed when the music calls for 3-part harmony.  Boys don't always sing melody.  It's not anyone's fault that you can't read music.
Next point:  When the worship director asks everyone to stand up at the beginning of practice, it's helpful for everyone if you don't mutter under your breath, "Yeah, that's not happening."  Your bad attitude and unnecessary comments are...well, unnecessary.
Finally, extending on the first point, not only are you not required to sing in the voluntary choir for Easter service, but also it's just not about you.  It's about praising God and celebrating that His son rose from the dead.  For me.  For you.  For us all.  Because we are all sinners.  He erased your sins.  He washed my sins away.  And if He didn't send His son to die for us, I would be so lost.  And I wouldn't have anything to sing about on Sunday morning.
So please, on Sunday morning, could you possibly show up at 7:30, ready to give Him the glory and praise for what He has done?  Just make it about that. 
Wear some comfy shoes so you don't feel like you'd rather sit on the bleachers while you sing, mmmm-k?
Thanks!
Love,
Beth