Someone who is an atheist but has a wide knolegde of science and religion. The evangelical atheist has choesen science over religion with good arguments as to why he or she has done so. It is basically a religion without a god.
(Looking at some of the other definitions i decided to post a half decent one. The other ones seem to look at evangelical atheists as assholes... that is not true. You will encounter some but at least they put forward logical arguments about their view unlike religious people. "Yeah well god said let there be light and it just appeared..." makes perfect sense.
Evangelical atheist - Hey im an atheist :D
OMFG WTF LOL UR OBVIUSLYY GHEY COZ ITS TRU DAT GOD WOZ MAKE DA WORLD COZ IT SEZ IN THE BIBLE SO UR RONG LOL