smart al·eck 
(ălĭk)
(ălĭk)n.
Informal
Informal
A person regarded as annoyingly self-assertive, especially for making impudent displays of knowledge.
[Perhaps after Aleck Hoag, 19th-century American confidence man and thief.]
smart-al′eck, smart-al′eck·y (-ĭ-kē) adj.