Green’s Dictionary of Slang

c.b. n.2

[abbr. SE clitoris + boner n.4 (1)]

(US campus) of a woman, extreme excitement, usu. sexual.

[US]P. Munro Sl. U. 102: I totally had a C.B. when Josh came into the room | I got a C.B. when I got my midterm back with an A on it.