Somebody who commits acts of sexual intimacy with dromedaries or bactrians. An especially horny and sex-starved desert traveller, or a total perv.
Also an annoying person resembling the above.
When the new recruit arrived at the desert base, the sergeant told him to keep his urges under control, but when he got too horny, he should use the camel in the shed. After a month his balls were fit to burst and he went in there and fucked the camel every which way. When he came out he asked the sergeant if he did it right and the sergeant said to the camelhumper, well, the other guys just ride it to the brothel in the next town.