I used to introduce myself as 'an unaccomplished singer', everything was a capella.
How about 'The Butcher Boy'? I used to do that, but it would probably be more powerful sung by a girl.
You can also do a really killing version of 'Johnny, I hardly knew you'. Goes like this:-

Start by singing 'When Johnny comes marching home' slowly....

When Johnny comes marching home again, hurrah, hurrah!
We'll give him a hearty welcome then, hurrah, hurrah,
Oh the men will cheer, and the boys will shout,
And the ladies they will all run out,
And we'll all be glad when...........

Going the road to sweet Athay etc

Use the verses in order, ending with:-

You haven't an arm and you haven't a leg huroo, huroo,
You haven't an arm and you haven't a leg huroo, huroo,
You haven'n anrm and you haven't a leg
YOU'RE AN EYELESS BONELESS CHICKENLESS EGG!
Ah you'll have to be put with a bowl to beg,
Johnny I hardly knew you!

Normal chorus next, leading into...sung slowly...

When Johnny comes marching home again, hurrah, hurrah
Who'll give him a hearty welcome then, hurrah, hurrah,
WITH ONE GOOD LEG AND ONE EYE GONE
AND BLOODSTAINS ON HIS UNIFORM
Will we all be glad when Johnny comes marching home?

Work up a good head of anger in the last verse and the reprise. and you should finish up with someone in tears!

FC