OT: Do you respond to all PM's?

Do you always respond to private messages that other forum members send you here on MR?
Do you respond even if you don't particularly care about that member, or do you ignore PM's from members that you don't like, even if their being civil and friendly with you in that PM?
Do you respond even if you don't particularly care about that member, or do you ignore PM's from members that you don't like, even if their being civil and friendly with you in that PM?