Green’s Dictionary of Slang

smarty-pants n.

also Miss Smarty-drawers, smarty-boots, -britches, -drawers, smartiepants, smartipants, smartboots, smartpants

1. [1930s+] (orig. US) a general term of usu. light-hearted abuse.

2. attrib. use of sense 1.

3. as a term of address, usu. negative.

4. [1940s–50s] (US black) a young man at the outset of his sexual career.