cynical

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Believing or showing the belief that people are motivated chiefly by base or selfish concerns; skeptical of the motives of others.
• adjective Selfishly or callously calculating.
• adjective Negative or pessimistic, as from world-weariness.
• adjective Expressing jaded or scornful skepticism or negativity.

from The Century Dictionary.

• Same as cynic, 3.
• Having or showing a disposition to disbelieve in or doubt the sincerity or value of social usages or of personal character, motives, or doings, and to express or intimate the disbelief or doubt by sarcasm, satire, sneers, or other in-direction; captious; carping; sarcastic; satirical: as, a cynical remark; a cynical smile.
• Synonyms Pessimistic, etc. (see misanthropic), morose, sarcastic, satirical, carping, censorious, snappish, waspish.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective of or relating to the belief that human actions are motivated only or primarily by base desires or selfishness.
• adjective skeptical of the integrity, sincerity, or motives of others.
• adjective bitterly or jadedly distrustful or contemptuous; mocking.
• adjective showing contempt for accepted moral standards by one's actions.
• adjective medicine, rare like the actions of a snarling dog.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective believing the worst of human nature and motives; having a sneering disbelief in e.g. selflessness of others