Today's politiquette tip: don't tell a person using a wheelchair, "I don't think of you as someone in a wheelchair!" Or more commonly: "I don't think of you as a minority!" said to people of color. The implication, of course, is that the listener has managed to transcend being from a group of less-thans, and the speaker is, of course, congratulating himself or herself.
Exception to this rule: lawyers seem to love to be told, "You don't act like a lawyer!"
If this is confusing, watch this funny video: "If Black People Said What White People Say."