I've never met an "agressive" atheist in person only on the internet. However I think that term might need to be defined.
characterized by or tending toward unprovoked offensives, attacks, invasions, or the like; militantly forward or menacing: aggressive acts against a neighboring country.
making an all-out effort to win or succeed; competitive: an aggressive basketball player.
vigorously energetic, especially in the use of initiative and forcefulness: an aggressive salesperson.
boldly assertive and forward; pushy: an aggressive driver.
emphasizing maximum growth and capital gains over quality, security, and income: an aggressive mutual fund.
a person who denies or disbelieves the existence of a supreme being or beings.