The word is usually used to express annoyance, disgust, surprise, anger, irritation, contempt, or disappointment...usually in a light-hearted manner.
(Lately, this word has been favorably used using squinted eyes, a scrunched nose, and a whispery, whiny voice, all while hunching the back slightly and is usually followed by the recipient with the traditional slow shake of the head, a stupid smirk and the low mutter of the word "geek.")
Alor: "Hey Eyuel, Samora forgot Madden at home."
Effers Example 2:
Melaku: "Hey you guys, my mom said we have to leave cuz its getting dark and she wont be able to find me so I have to take the ball now."
Aklil: "But it's only 5:30! You won't disappear until 9!"
Effers Example 3:
Alor: "Hey Joseph, can I borrow a dollar?"
Alor and Joseph: "..the heck?"
Eyuel feels stupid.
Yeah. Bitchy like hell.
B2: You Effer! Give her back!
B1: She's effin' hot, and so I won't, Effer.