Like any missionary, except one who preaches out of the book of (Karl) Marx.
Basically, any communist in your workplace or
college.
They believe in overthrowing the superior western system of capitalism, and replacing it with what is essentially surfdom - basically,
people working in the fields and factories all
day for virtually no personal gain.
They are annoying, and like most cultish preaching missionaries, they speak some
real non-sense, and are hard to get rid of.
And like Scientologists, they will make your life a living hell if they find that you have anything against them.
"Agh! Help me get rid of the Marxist missionary, they
keep preaching about revolution, and
won't listen to any of my
logic!