If something's repulsive, it's so disgusting you don't want to go near it. You may find rotting meat repulsive, but maggots find it delicious.
In the early 17th century, the word repulsive simply meant something that repelled or "pushed away." For example, the like poles of two magnets are repulsive to each other, pushing each other away. Today, repulsive usually means disturbing and sickening. As manners guru Amy Vanderbilt said, "Do not speak of repulsive matters at the table."