Closet racism usually is never done within earshot of anyone of a different race.
Closet racists can like music and culture of another race, yet dislike another race simply because they don't like the color of their skin.
For example, a guy after a few beers with his friends starts to tell a few jokes and have some manly moments all within the confines of their circle.
One sure sign of a closet racist is when they e-mail you an ethnic joke with this preceding "I'm not racist, but...I found this amusing"
Get away from me, man. You're spewing closet racism.