meaning : da fuck
df means almost the same thing as "wtf" but,it's more flexible and,you can use it in more than one way.See example.
Cisco:"D00d,that fucking car almost ran me over !"
Mike:"Yeah man,df kind of driving was that ?!"
Example # 2
Cisco:"Your mom was blowin' me real good last night ! XD"
Mike:"df dude !"