when pigs can fly

The phrase, "when pigs fly," means never.

The phrase might be suitable in a situation when an obnoxious man is pursuing a woman in an obnoxious manner.

Example:

Obnoxious man: "Hey baby, when are you and I getting together?"

Woman: "When pigs fly."

It is NOT a phrase that you would use to reject someone's love if you care about that person's feelings.

when pigs can fly
Certainly, but it should be done with gentleness and tact.

when pigs can fly
OOPS! I meant certainly NOT! It would be rude and unkind.