Leukophobia

Listen up, buttercup. This joke is for people that don't understand things. Leukophobia, which sounds like "look-o-phobia," is actually the fear of the color white. But the joke is that it sounds like "leuco-phobia" which is fear of semen! So, people who are afraid of white stuff won't have sex because semen is white! You probably think semen is mayonnaise, don't you?