Finger Picking Intro:

E---------------------0-------|
B-----------------3-----0-----|
G-----1-----2---2-------------|
D---2-----2---0-----------4---|
A-------0-----------2---------|
E-0---------------------------|
  E     A     D     B

E            A        D             B
She's got a smile, oh she's got a smile
E          A                 D      B
And she's flashing it right at me

She's got a wink, a wink across the bar
and I know that's meant to be.
She's got a walk, oh she's walking over
and I think this could be my day.
She's got a ... friend, oh she's a got a friend
Why she standing in her way?
Its a big fat friend...

Chorus:

E--0---0---X---X--|
B--0---2---5---X--|
G--1---2---4---4--|
D--2---2---2---4--|
A--2---0---X---2--|
E--0---X---X---X--|
   E   A   E?  B

-strum E A E? B

Oh God there's always one (Big fat friend)
To spoil my f**king fun.

Now baby baby baby if its boots you want to knock
Leave your chubby friend at home because she's gonna
block the c**k
Now I'm afraid of no man, with any I'll contend,
E                  B
But I cannot compete with your big fat friend

Back to Finger Picking Intro:

So big fat friend, ah we meet again,
You won't leave her alone
you roll your eyes, make sarcastic comments 
while you're sucking on a chicken bone

Strum Intro Chords:

But that's okay, you think you won the battle but I tend to disagree
See I know you, and your Achilles' Heel and he's standing next to me
My non-discriminating friend...

Back to Chorus:

So what that you're a cow (non discriminating friend)
I'll nail you any how. {Hold B}
I know that he's no looker and he's had a couple rounds
But for every shot of Jeger hey you lose a couple pounds. {Hold B}

Now baby baby baby bring the evening to an end
E                        B
Just you and me and my pal and your Big Fat Friend

Outro:

E-------------4-----3-----2------X----|
B---------------5-----4-----3----4----|
G--slide to 4-----4-----3-----2--4----|
D--------------------------------4----|
A--------------------------------2----|
E--------------------------------X----|
                                 ^end on B

Well that's the best I can do.  This is my first tab, so hopefully it's understandable.

Credit to "ParrotEMT (aka Buddascotchpuddin!)" for the lyrics.