To not share my pizza?

[GoudaMozzarella]

Every time we have homemade pizza, DP eats his faster than me and then wants a slice of mine (he always thinks I won't eat it all). Am I being unreasonable to say no? He knows how much I love my pizza. After he sulked when I said no tonight, I did relent and offer him a piece since I wasn't going to finish it but he said he didn't want it anymore and said he's taking the moral highground.
I told him I'm taking it to mumsnet and he told me that I am "going to get battered by the mums". Am I being unreasonable to want to keep my pizza for myself?

@INeedAnotherName ha! Yes, I do freely admit to it, but I 100% wouldn't do it if she minded! It's clearer with pizza (esp takeaway) because we might have actually chosen different toppings according to preference so that's what makes it 'hers' or 'mine', but normally all our food is communal and placed in the middle of the table. So we often ask each other how much of a second helping we're planning to have, to make sure enough is left for everyone.

Actually it's a moot point because all our food is now hoovered up by our even greedier toddler.