Mark plays this part all the way through the song:

E|------------------------------|
B|------------------------------|
G|-------------------------5----|
D|-5-5-5-5-4-4-4-4-2-2-2-2-5----|
A|-5-5-5-5-4-4-4-4-2-2-2-2-3----|
E|-3-3-3-3-2-2-2-2-0-0-0-0------|

[I'm gay.
So what?
Don't judge.
My butt.]

In the second verse Tom joins with this:
(I just noticed that Tom plays it on the D string but i'm too lazy to change it.)

E|------------------------------|
B|------------------------------|
G|-0-0-0-0-0-0-0-0-0/2-2-0------|
D|------------------------------|
A|------------------------------|
E|------------------------------|

E|------------------------------|
B|------------------------------|
G|-0-0-0-0-0/2-2-2-2/4-4-0------|
D|------------------------------|
A|------------------------------|
E|------------------------------|

[I'm gay.
So what?
Don't judge.
My butt.]