Pineapples

Means to stop, quit or more specifically drop the topic.

When someone says Pinapples you better stop talking about what you're talking about before the situation escalates.

Rather than being rude and saying "shut the f*** up", it's a nicer more subtle way to say the same thing.

Jose:

"I don't care about that dumb girl and I will make her life a living hell for what she did...."

Vicki:
"PINEAPPLES!!!
PLEASE, PINEAPPLES"