"breasts," 1929, U.S. slang, probably from much older term boobies (late 17c.), related to 17c. bubby; perhaps ultimately from Latin puppa, literally "little girl," hence, in child-talk, "breast." Or else it is a natural formation in English (cf. French poupe "teat," German dialectal Bubbi, etc.).
A blunder; error; boo-boo
: If I boob, I expect you to protect me (1930s+)