1.  n. an obnoxious person. (Rude and derogatory.)  You silly birdturd. Wake up!  
2.  mod. stupid; obnoxious; lousy; worthless. (Usually objectionable.)  Of all the stupid, underhanded, birdturd tricks—this takes the cake!  
3.  n. bird dung, especially if dried. (Usually objectionable.)  There’s birdturd on your shoe.