Wow...I could so see myself with the ranting about an argument or debate at work when I get home. Especially during PMS. Well, and having an idiot for a boss helps too (I found a new job, thank God.)
But more to the point...as an ISFJ, here are my suggestions: Just listen to us. Say things like "That sounds frustrating" and "I'm sorry you had to deal with that" and if you do disagree with the "debater" on the other side, make it loud and clear! "That was really rude of her to say!" or "I canNOT believe she did that." After letting them blow off steam for a little bit, like everyone else said...distract them! Suggest something fun to do together. Tell them a joke you heard. If it's your significant other...after some time, say "Well, I think you're amazing...Hey, what do you want to do this weekend? Jim and Sandy invited us.....etc..." It's also a good time to bring up nice things that people have told you about them. "I forgot to tell you...I saw my friend Sarah the other day and she told me that she thinks you're really smart." DON'T make stuff up or be patronizing, cuz we can tell.
With regard to us complaining or having a pity party -- I hate to say this, but I've been around many different personality types and everyone does it at one point or another...we all have our times! I remember when I was dating my INFP boyfriend...I would call him when I was feeling down and he would always say "I'm sorry that you're down...I'll be over in a few minutes and we can go get some ice cream." It might not be good on the waist line (but we can exercise it off...and exercise helps us feel better too!), but it worked wonders for me. My husband (who is an amaaazing INFP) knows just when to bring me chocolate. He also knows just when to say "Hey, you seem down...let's go for a walk and you can talk about it." This is a genuis idea..because walking gets the endorphins going and once I've vented and the endorphins are going, I feel better than ever when I get back from the walk!
I would also say that I tend to hold things inside because I don't want to "bother" other people, so when I get down...I usually have many reasons that I just haven't articulated...and they can be big things. My 5 year old niece died 3 years ago and I get sad every year on her birthday. I won't tell anyone though...so some people might think I'm sulking or pouting or whatever...when in reality, I just miss my niece. I personally like my own space to deal with those things, so when my husband goes to play soccer or takes my boys for ice cream (those INFPs love their ice cream), he gives me space to work through things in my head and get myself back into a better place. I eventually will and I'll come back to normal. If he tries to get me to feel better or accuses me of being "whiny," I will fly into a rage and he won't know why until later (and then he'll feel really bad, because he understands me being sad about my niece.)
And my INFP can get himself into big long funks sometimes as well, that last longer than most of mine. He has been complaining about his job for years and years and gets so unhappy on Sunday nights when he has to go to work the next day. He wants to be a writer and be creative, but he always seems to lack the follow through to figure what he wants to do and then make a change. I reminded him of the serenity prayer "Accepting the things we can't change, having the courage to change what we can and knowing the difference" that he will sometimes remind me of when I'm getting down. Compassion goes a long way.
I have a question: Doesn't it seem like most things in life that upset us have to do with control? Whether it's control of ourselves or control of situations or control of others....it always seems to come back to control. Just my little philosophical thought for the day.