In the English language, I can't think of any way of calling somebody a pig (das Schwein) without it sounding pretty insulting. It's also usually the case in German that labeling someone a Schwein is meant to express disdain or to be purposefully offensive:

Du bist so ein Schwein geworden. Und wir waren mal Freunde?

You have become such a pig. And we were once friends?

Caption 17, Die Pfefferkörner - Eigentor

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BANNER PLACEHOLDER

Und damit kann das Ziel

And with this, the objective

des Attentats doch noch erreicht werden.

of the assassination attempt can still be reached.

Wenn das Schwein wenigstens tot wäre.

If the swine was at least dead.

Captions 27-28, Die Stunde der Offiziere - Dokudrama über den 20. Juli 1944 

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Du Schwein! Raus hier, du Lügner!

You pig! Out of here, you liar!

Caption 31, Filmwettbewerb "filmreif" - Mama mach die Augen auf

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Unser Chef ist ein mieses Schwein.

Our boss is a mean pig.

Caption 41, Weihnachtsfilm - Ein Sack voll Geld

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In German, however there is at least one slang context where Schwein is used together with the adjective arm ("poor") to express sympathy for somebody's situation:

Der Mann ist obdachlos.

The man is homeless.

-Das arme Schwein! Vielleicht sollten wir ihm eine Spende geben.

-The poor swine! Maybe we should give him a donation.
 

In English, this is the equivalent of saying "poor bastard," or the rather old-fashioned "poor devil." It's still common in British English to hear the similarly inclined "poor sod." None of these words are very nice, but they're used nevertheless to express sympathy!

Schwein haben is also used as an expression for having had good luck: 

Und permanent stand ich mit einem Bein

And I stood permanently on one leg

im Knast, doch meistens hatt ich großes Schwein.

in jail, but mostly I was very lucky.

Captions 23-24, Frank Zander - Tu doch meine Asche in die Eieruhr

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If you didn't know this expression, you might wonder about him having had "a large pig" in prison!

Another nice idiomatic use of Schwein is when you don't know anybody at a place or event: 

Hier kenne ich kein Schwein.

I don't know anyone here.

In this context, kein Schwein essentially means "no one" or "nobody":

Kein Schwein war da.

Nobody was there.

Wenn man sagt: „Kein Schwein war da“,

When you say, "No pig was there,"

dann möchte man ausdrücken,

then you would like to express

dass man zu einer bestimmten Zeit an einem bestimmten Ort war

that you were at a certain time at a certain place

und dort überraschenderweise niemanden angetroffen hat.

and, surprisingly, met no one there.

Captions 42-46, Eva erklärt - Sprichwörter

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Further Learning
Go to Yabla German and see some other uses of das Schwein in a real-world context.