It is a term used largely in the British Army where new recruits or private soldiers are forced to brew up for lance corporals, corporals, sergeants etc... Skiffing the tea makes the tea brewer feel better about having to make the twat some tea in the first place.
"Jones, make four brews, unskiffed!"
"Did you skiff the corporal's tea?"
"Don't drink that I've just skiffed it."
Skiffer: "Oh hell yeah man, im down for it whenever!"
F:"Really? Ive got some right now, lets toke up!"
S:"Oh, I uhhh... have some things to do right now... And i just remembered that ill be out of town this weekend..."
F:"Come on man, you skiff out on me everytime."
S:"Hey, ill do it when im ready."
F:"Youve been saying that for the past year and a half now..."
2.) The act of purposely excluding one from a conversation, usually while the person is standing right there.
Blake: "Who's Rachel?"
James: "Terry, she was looking fresh! I definitely wanna tap dat."
Blake: "Guys, who is Rachel?"
Terry: "James, you ain't going to tap that before I do!"
Blake: "Please don't skiff me...."