These may or may not be correct, as I don't follow Harry Potter and a lot of the words are kind of muffled:

Oh hey there, Severus
What can you do?
You're facing a rebellion
That's sending you shampoo

Graffiti in the hallways
The revolution grows
But how can we expect you
To see it past your nose?

You thought that you would move on from potion's master
But you don't have a school
You've got a disaster

Tryin' to stop us has you at your wit's end
'Cause your ugly little sidekick
Can't compete with friends

Oh hey there, Severus
What will you do?
We've taken on Alecto
And Amycus too

You know who is breathin' down your back
But we're two steps ahead of you on every attack

Oh hey there, Severus
Professor Snape
You laid the trap
But we made our escape

The room of requirement won't let you in
But we'll be back soon
And the real fun will begin

Oh hey there, Severus
Say goodbye
You know when you've gone
Oh, we're not gonna cry

We're sending you a farewell card
That's sealed with a hex
Avada kedavra
XOXOX

Oh hey there, Severus
Severus snape
Oh hey there, Severus
Severus snape

Listen now, Severus
Severus snape
Oh listen now, Severus
Professor Snape