Literally "that would be sausage to me", this expression is used to say that you couldn't care less about something. Note that you cannot use it to say that you don't care about somebody. Often the "mij" becomes "me". You will also hear "dat zal me worst zijn".
Check out the comments to this post for a discussion on the use of 'wezen'.
– "De Giro d'Italia start in Amsterdam dit jaar!" – "O ja? Dat zal me worst wezen, wielrennen boeit me niet."
("The Giro d'Italia starts in Amsterdam this year!" – "Really? I couldn't care less, bicycle racing does not interest me at all.")
– "Dit kun je toch niet maken man? Asociaal!" – "Ik doe waar ik zin in heb, OK? Wat jij van mij vindt zal me worst wezen!"
("You can't do this / be serious about this! That is so rude! – "I can do what I want, OK? I couldn't care less about what you think of me!")
– "Heb je je targets van dit jaar al met je manager besproken?" – "Targets? Dat zal me allemaal worst wezen, want iedereen wordt toch ontslagen door de crisis!"
("Have you already discussed this year's targets with your manager?" – "Targets? I couldn't care less about my targets because due to the crisis everybody will get the sack anyway!" Note that when the Dutch use management terminology it is often in English.)
– "Wat kan mij het schelen!": what do I care!
– "Dat kan me niet rotten": I couldn't care less [informal].
– "Boeien!": Boring / not interesting at all / I so not care etc… The verb "boeien" translates as "to fascinate/captivate".
– Worst: sausage [noun] [de worst, de worsten].
– Saucijzenbroodje: 'sausage roll' [noun] [het saucijzenbroodje, de saucijzenbroodjes]. Popular Dutch snack that you can often buy in department stores or at train stations.
– Slager: butcher [noun] [de slager, de slagers].
The "HEMA" is a popular department store in the Netherlands, where you can buy almost anything of reasonable quality at a reasonable price. This includes the famous "HEMA rookworst": HEMA smoked sausage. Although the Dutch are not really 'sausage minded' (as some people would say of the Germans) the HEMA rookworst is a popular snack amongst the old and young. After having successfully expanded to Belgium, HEMA tried its luck in Germany. Soon the number one selling item was… the rookworst!