Have you ever met a joyless Calvinist? How about a rigid one or a mean one? Have you encountered someone who is ready to go to war over the Doctrines of Grace while never seeming to exhibit the very grace he so vigorously defends?
Arminians would say the problem is in the doctrine of Calvinism itself, and to be sure many Calvinists give credence to such perceptions. John Newton once wrote:
I am afraid there are Calvinists, who, while they account it a proof of their humility that they are willing in words to debase the creature, and to all the glory of salvation to the Lord, yet know not what manner of spirit they are of. . . . a man may have the heart of a Pharisee, while his head is stored with orthodox notions of the unworthiness of the creature and the riches of free grace. -- “On Controversy,” in The Works of John Newton
The problem isn't Calvinism, because mean-spirited rigidity finds a home in every denomination and theological stance. The more one knows theology (any theology), the greater the temptation of becoming prideful. Paul warns us that "knowledge puffs up" (1 Cor 8:1). There is nothing wrong with knowledge in and of itself. In fact, the Holy Spirit even gives some the gift of knowledge. Jesus came to give the "knowledge of salvation to his people" (Luke 1:77) and condemns those who "take away the key to knowledge" (Luke 11:52). But knowledge in the unconverted or spiritually-weak heart can only produce arrogance.
Simply put, the "angry Calvinist" isn't a believer, or at the very least he is a rather pathetic one. He may be a champion of orthodoxy, but something hauntingly Pharisaical hides beneath his theological veneer. Jared Wilson offers this wonderful illustration:
A joyless Calvinist knows the mechanics of salvation (probably). But he is like a guy who knows the ins and outs of a car engine and how the car runs. He can take it apart and put it back together. He knows what each part does and how it does it. A graceless Calvinist is like a guy who knows how a car works but has never driven through the countryside in the warm spring air with the top down and the wind blowing through his hair.