Thomas Midgley, Jr. Invented Leaded petrol to stop knocking as well as the first CFC's to stop refrigerators from killing people. These were both real helpfuks.
The charitable consent to having sex with a less fortunate/ugly/awkward member of the opposite sex. Usually done at the request of the helpfukee's friends.
Tom walks into a shady bar with his ugly friend Bobby. After a few drinks, Tom walks up to the drunkest, sluttiest girl in the bar. He explains that his friend Bobby is extremely awkward with women and hasn't been laid in months. He then asks the girl if she could his friend Bobby a huge favor and agree to a helpfuk. A few minutes later, the girl takes Bobby home and has sex with him.
Someone who appears to be helpful but really is not helpful at all. Gives you more information than you had previously but not enough to do anything with it.
The IT guy is such a helpfulasshole. He told me he knew how to fix my email but he has no intention of fixing it.