A brother who, due to an incestuous relationship between one's parents, is also a male first cousin.
My brothercousin Cletus done gone stole my meth.
person who you assume has mental disabilities due to genetic problems from being inbred, you assume they are simultaneously someone's brother and cousin.
'man that guy has been trying to push open that pull door for like 3 minutes.'
'he's a brothercousin, no doubt.'