1. [1950s+] (orig. US teen, also zat, zitz, zort) a spot, pimple or blackhead; also attrib.
2. [1960s] (US campus) any form of mark.
3. [1960s] (US campus) a general insult.
4. [1960s] (US gay) an underage boy.
5. [1970s+] a skin blemish left by a lovebite.
[1980s] (US teen) a dermatologist.
[1990s+] a general term of abuse, delivered to one who has acne.
[1990s+] (US) a teenager, the image is of acned mediocrity.