So you'd be perfectly happy if your DH ate, say, all of your birthday cake, and you hadn't had a slice? or if you had a bought some nice ice-creams for the family, and you went to have yours and they were all gone, because DH had seen it and eaten it?
As for the crisps, if you went and bought 12 packs of crisps instead of 6 packs, and DH ate them all in one week, and left you none, you'd just smile happily and buy 18 packs of crisps the next week and so on?
And in reverse, your DH would never grumble if you did the same thing to him?
Would you eat an entire packet of biscuits, knowing that no-one else in the house had had any? You wouldn't think "Oh, I'll save this last penguin for Mr Banana, he hasn't had any yet"? or go "Oh, my there's only 1 pack of crisps left... whoops... How many have I eaten... 5? Oh I better see if Mr Banana wanted the last pack before I eat them" or
would you just go "fuck it, you snooze, you lose" and eat them..
To me that is selfish behaviour. It's not about how many packets of crisps anyone is "allowed" or what is a reasonable time frame. It's the not thinking of others whilst satisfying yourself that is the issue for me.