For a male who has a curved penis it is the act of taking two bibles (one in each hand) and slamming them on your penis to straighten it out. Named for the resultant thump that is heard when slamming.
"After years of masturbating my penis leans to the left."
"Go bible thumping, that'll straighten it right out."
I an atheist whos only argument for the nonexistence of God is to persuade you in a forceful and enthusiastic way that Christianity and the Bible are wrong.
He is a Bible thumpingatheist who thinks if he invalidates Christianity, that he can disprove God.