1. piece of cake [noun] [het inkoppertje, de inkoppertjes] [‘in-ko-pur-tju’] 

The verb "inkoppen" is literally translated with "to head in". "Inkoppertje" is the diminutive of the noun for the act of heading something in. The term is taken from football/soccer jargon, where an "inkoppertje" is a goal you can’t miss by heading it in. Outside this context, the phrase is used when something is very easily accomplished or solved by the person who then uses the phrase.

Examples:
– "Hoe ging je examen Nederlands?" – "Inkoppertje."
("How did your Dutch exam go?" – "Piece of cake.")

– "Als ik zeg: ‘Alle mensen zijn sterfelijk; Socrates is een mens’, wat zeg jij dan?" – "Inkoppertje jongen: dus Socrates is sterfelijk."
("When I say: ‘All human beings are mortal; Socrates is a human being’, what do you say then?" – "Piece of cake, dude: thus Socrates is mortal.")

Related words:
– "Inkoppen": head (the ball) in(to the goal).

Example:
– "De spits kon de 3-0 zo inkoppen."
("The forward could easily head in the 3-0.")

Related expressions:
– "Fluitje van een cent": piece of cake.
– "Appeltje, eitje": piece of cake.

2. a very easy win, easy point [noun] [het inkoppertje, de inkoppertjes] [‘in-ko-pur-tju’]  

Subtle difference with the first translation (see 1.) is that in
this context the phrase is used when someone
indicates that something is very easily done-said for another person.

Examples:
– "Je ben gisteren en eergisteren uitgeweest?? Daarom zie je eruit als een dweil…" – "Ja, ja, inkoppertje…"
("You went out last night and the night before?? So that’s why you look like crap…" – "Yeah, yeah, easy point (for you)…")

Related words:
– "Makkelijk": easy.