For those of us who don't speak drunken Scotsman, This was written in response to Burns' spying of a louse on a fine lady's bonnet during church. She is most likely sitting in the front pew, with all of the poorer classes in the back of the church. Burns is behind her, spots the louse, and realises everyone else will see it.

The whole point of the poem is summed up in the lines "O wad some Power the giftie gie us / To see oursels as ithers see us!" or, we should be able to see ourselves the way others do, then maybe we wouldn't act like such jerks. Burns was a big fan of sticking morals in the end of his poems; see also "To a Mouse".

Jenny, the girl in the poem, doesn't know the louse is there, so she will continue to look down her nose at all the lower-class citizens, even though they now know she's no better than they. She has lice too.

Here is my translation, it doesn't rhyme, but semi-accurate translations rarely do.

Hey! Where are you going, you creepy-crawly?
Your arrogance is no protection
You don't usually hang out
On such pretty and expensive fabric
I think you don't usually feed on chicks like that

You ugly, creeping, blasted bug
Hated, rejected by both saint and sinner
How dare you crawl upon her?
This fine lady?
Go somewhere else and seek your dinner
On somebody poorer

Go! To some poor beggar's house
There, you can be creepy and gross
With your own kind, out in the country,
Where no one will try to get rid of you

Well, at least hide! Get out of sight
Below the ruffles
Oh man, you won't stop,
Until you're on the very top of her bonnet

I wouldn't have been surprised to see you
On some old lady
Or on a poor and dirty boy
But on this lovely girl?
How dare you!?!

Oh, Jenny, move your head.
Knock that louse off
You can't see how visible he is
But all the other churchgoers can

Oh, if only some power would give us
The gift to see ourselves as others see us
It would free us from blunders
- That's crazy talk
Most of us are such snobs about the way we dress, 
and act, and even where we sit in the church.