Religion-crazy believers, usually Christians. Those who can never shut up about how "great he is" and how everybody will go to hell who do not practically come about the Christian religion.
When one of our highly religious friends randomly start up an annoying, uncomfortable conversation of "how great church was last night" and how "my life was enriched by the holy saviour" ... by now Nic* & I just go: "dude, we don't jizz for jesus."
Henceforth, a Jesus Jizzer is the exaggerated word for jesus lover. It's like the Christian exaggeration for the word atheist is Devil Worshipper.
:P simple as that
A person who is so religious, they want to slam it in your face any chance they get. You can often tell even from their bumper stickers. These people are said to be "jizzin' for Jesus."
"Aww, man! They have the fish on their trunk AND they're going slow. Damn Jesus Jizzers!