I almost always accept. But if I completely high rolled my opponent in the game that resulted in a friend request. I either accept and walk away for a few min. That way they can yell their lungs out as much as they want if that is their goal. Or I wait a couple hours before accepting. That way they can get the salt out of their system.
I however never accept a friend request that comes in lightning speed after I won a game and my opponent spammed the threat emote the last few turns.
It just make my skin burn when people feel the need to flame you to death after they lost a game. So I try to avoid that as much as possible. I mean. Everyone can get mad at the game sometimes. But there are no point in flaming your opponent for playing the cards he or she was dealt.
That being sad. I have meet many very nice people, so I do like to add people more than not.