It's much easier when you let Merriam-Webster pick your friends.

<well i try to phase it out. if they're close enough, i will tell them if something they did upset me. if they acknowledge and we resolve it, cool. if not, then its an indication to me that they are not capable/interested in working things out with me. then there's nothin to resolve, i simply focus my energies on people who are more deserving of it.>

wise words!
I've had occasion to cut a couple of friends and half my family out of my life. You can try to communicate and sort things out, but as people are posting here, sometimes that person is incapable or unwilling to make the necessary compromises that make up a true friendship. Phasing them out is gentle and honest. You don't make up lies to avoid them, you simply make other plans that include more responsive people than the difficult "friend". It's very important to be real with your longterm-but-challenging friend. Seniority does count for a lot. You have to make sure that it's more than just a rough patch of the relationship before you go ostracizing them from your life. The first step of phasing them out, to my mind, is to stop finding them jobs or supporting them financially in any other way. A true friend is not a financial vampire!

When you know you should call them, but you just can't or don't have the energy any more.

You want to give her up but you can't
You are able to give up other friends
She loves you and vice versa

If you also kinda think she's hot -- you may be in love.

A dear and wonderfully functional friend once told me that if I'm ready to get rid of a friend, its a great time to practice my communication skills.

When you _________
I feel _____________
What I want is __________

The worst case scenario is that she doesn't respond and the friendship is over. Which it will be anyway if your needs are constantly trampled.
Some friends challenge us to grow, some we just grow out of. Ultimately its up to you what price you are willing to pay to keep the friendship.