I don't think you are petty and mean-spirited, I think you are human.  And maybe a tad competitive?  I know I get like this occcasionally (ok, ok more than occasionally) and it is usually when I am feeling a tad too competitive in the lab-even when there is nothing to be competitive about.  And hearing about it all day doesn't help any either.  It happens to the best and worst of us.

This is normal DGT. Don't be so hard on yourself.  Don't try to force yourself to feel differently or feel something you don't. Allow yourself the feelings and then let it go.

 In industry labs (that I've been in), this type of competition in a team doesn't happen. I have to say, it's nice.  Part of it is that we all work together so much that the idea that might have worked often came from someone else.

I think your experience brings up a good point about mentorship in academics. Do you think that when someone in a group gets heaped on with a lot of praise, that the PI should make sure the others on their team are not feeling dejected? Maybe the PI should give the others a boost? Or is this process of being on a roller coaster of emotions just part of the culture?

As the others have said, jealousy is normal.  Especially if you are competitive or haven't had some praise for your work thrown your way recently.  I tend to go bitch to some friends outside the situation and then use it as motivation to kick butt in lab and get some of that recognition for myself.  Cuz I like the spotlight (in lab).

I agree with all the other posts here.  You're entirely human and normal to be envious of your lab mates success.  You should see it as a good thing that you are able to swallow those emotions and congratulate the guy and that you're frustrated with yourself for feeling this way about him and his success.  Don't lose any sleep over it, you're time will come and as everyone else has said use it as a positive motivational tool to get you focused on your project again.  At least now you have something to strive for, you know that when you get good data you're going to get such good feedback from others in your lab, not all labs are like that, feel lucky!

And the other pocket is full of envy!  

I suspect, DGT, that this is not your MO, but for the sake of discussion, I'm going to bring it up. Scientific envy is normal and can be motivational, as others have said... but you have to be careful that it doesn't turn you into a frienemy. You know the type--the colleague who smiles and says "Oh, good job", then tells people behind your back that "It's not that great"; or the labbie, who you consider a friend, making a catty comment about "who even cares" about your project; or the one that cuts all contact and doesn't respond to multiple messages even though hir Facebook status would indicate that s/he's alive and well. Science is hard... and a small, small world. Envy might be normal, but if you hold onto it, it turns into something ugly that can alienate you from your peers. And one day, you might just need those people.

Yeah, that is a good point. You don't want to become bitter and twisted, I hadn't thought about that.  Though as long as you manage to keep it internal and put it to positive use, then it shouldn't be an issue.