Templeton is just about as mean as they come. This wily creature cares about just one thing: his little rat self. All he wants to do is binge eat scraps from the farm or the fair. And he's not in the mood to help anyone out, even when Charlotte is dying. You might say he's the worst friend in the whole wide world.
Now compare Templeton's selfishness to Charlotte's attitude towards her friends. She's ready to help Wilbur no matter what. She even leaves her home, knowing she'll die at the fairgrounds, just so she can support her best bud. Now that's a friend. Templeton's focus on himself makes us realize just how much Charlotte puts her friends first and herself last.