I'm not sure you can do pure sarcasm in a non-offensive way, at least not if it's directed at the people you are talking to. Now, if you were in a group of people, and were sarcastic about some person not in the group, that might be funny, but it might also reflect badly on you.
"In sarcasm, ridicule or mockery is used harshly, often crudely and contemptuously, for destructive purposes. It may be used in an indirect manner, and have the form of irony, as in “What a fine musician you turned out to be!” or it may be used in the form of a direct statement, “You couldn't play one piece correctly if you had two assistants.” The distinctive quality of sarcasm is present in the spoken word and manifested chiefly by vocal inflection ...[7]
Hostile, critical comments may be expressed in an ironic way, such as saying "don't work too hard" to a lazy worker. The use of irony introduces an element of humour which may make the criticism seem more polite and less aggressive."
http://en.wikipedia.org/wiki/Sarcasm