I use negs/approval tactics with everyone. I am still quite generous but know when to stop. Recently one of my best mates has started taking the piss with me giving him stuff like beers and fags so I started negging him and he always reacts. Its hilarious.
http://www.youtube.com/watch?v=qy_mIEnnlF4 <Theres a good obviously comical version of what I do but I use words and some examples:
Friend: Oh hey man, can't make it tonight man.
Me: You're such a bellend mate, have a boring one on me.
Friend: Hey man I brought some beers and munch for us to chill.
Me: You fucking legend man!
Unfortunately ALOT of people have a "how will this benefit me" mindset. Shitty world we live in.