I'm a Christian. I'm proud of my faith, and I love the church. But sometimes my fellow Christians make me want to scream.

Like a couple days ago, when a restaurant server posted the following photo to reddit.

The story: The pastor was part of a large party who ate at this server's restaurant. Like many American restaurants, this particular one has a policy of adding an automatic 18 percent tip for large parties. It's something the computer does automatically, not something the server has any control over.

According to the server, the pastor's party tried to get around the automatic 18 percent tip by asking for separate checks, even though the same person was paying for the whole table. The server says that everyone was happy with the service; they just didn't like the idea of a compulsory tip.

The result? The pastor scribbled out the tip, leaving none at all, and adding the note, "I give God 10%. Why do you get 18?"

(As a side note, I suspect the server would have been happy with 10 percent of the diner's income as a tip. Only 18 percent of the cost of the meal is a bargain.)

Oh, and just to drive the point home, the diner made sure to add the word "Pastor" above the signature at the bottom.

Really?

In my book "TORN: Rescuing the Gospel from the Gays-vs.-Christians Debate," I argue that we Christians have often become our own worst enemies. In many communities, our reputation is that of uncompassionate culture warriors, quick to shout about gays or abortion or political candidates, but slow to show grace and mercy in our everyday lives. And these acts of ungrace by Christians have far more power to damage Christianity's reputation and influence than any attack launched at the church from the outside.