Eating expired ice cream is perfectly safe and should not cause you any sickness as long as the expired ice cream has been frozen and has not gone sour.
If the ice cream goes bad it will start to smell like soured milk would because ice cream contains milk.
You'll certainly be able to taste the soured ice cream if it is indeed bad and should be thrown out.
But just because the ice cream has went past it's expired or use by date it doesn't always mean that it's bad and unsafe to eat.
Just make sure it doesn't smell bad or doesn't taste bad and if it does then just throw it out to be safe.
If you do eat bad ice cream you'll likely get a stomach ache and just vomit the ice cream up and it should not cause anymore harm to you.