It's a cold world out there. One thing that always works for me is to share a positive, enthusiastic attitude.

Whenever I feel down, or when things aren't going my way, I try to instantly turn that around with a smile, a fun comment, or a positive action. Most of the time it works and as I do it, it becomes infectious, and bounces right back to me. So . . .

Email - Instead of replying to a snarky email, call the person up and get them to level with you.
Boss - Come in Monday with more energy and positivity than you've ever brought to work . . . ever. See what happens.
Clients - See how you can add just a little more pizzazz to every interaction. Call them unexpectedly and get their feedback.
Colleagues - See how you can help them. Givers gain.
Subordinates - Give them one of your higher-end projects. At first they might not like the additional work, but when they see the level of the challenge and the exposure to other people, places, and things, they will thank you.

As I stated from the start, the world is a cold place, so these tips might not work. So here's some advice — try one (or more) of them, if they don't work, you've probably run into one of three types of individuals:

Temporarily Bitter - Something has got them down. If your first attempts at changing their perspective fail, ask what is really keeping them down. Most of the time they will open up (which in and of itself helps) and allows you to spread some real warmth. This is your 'warmth' sweet spot.
Situationally Bitter - They hate a certain situation (their boss, their job, money, their clients, their life, their spouse/partner, their family, etc.). Attempt to help them, but you're treading in a minefield. Your warmth might be received as a shallow ploy to get something out of them. But it doesn't hurt to try.
Permanently Bitter - As I learned as a small child from the man who works on power lines: "Stay away, Stay alive." These are people that go through life spreading their angst, annoyance, and turbulent attitude to everyone they meet — they act like Ebenezer Scrooge without the epiphany. Unfortunately, these people need a lot of work and you have to decide whether you want to spend an inordinate amount of time investing in their transformation — and it usually doesn't work. Unless they are really close to you, it's better to find more appealing surroundings.

I find the more that you add warmth to every interpersonal interaction, the more you make the world a better place and enhance your reputation. Try it.

By the way, if you are really interested in being more positive, check out this book. It was given to me by my good friend and fellow coach, Steve Cary.