Venom: Whiniest. Supervillain. EVER!

Background (for those who might need it):

1. An immensely powerful being known as the "Beyonder" abducts many of Marvel Comics superheroes (including Spider-Man) and supervillians to another planet to fight each other.
2. After damaging his costume, Spider-Man discovers a "liquid" that molds itself to him and creates a new costume for him.  As a bonus, it also provides him with unlimited webbing and can mimic regular clothing, which allows him to change in and out of costume almost instantaneously.
3. The old adage "anything too good to be true, usually is" rears its ugly head.  The new costume is actually a symbiont (or symbiote, for those who, unlike my spell checker, prefer that spelling) that is controlling Spider-Man while he sleeps and forces him to go adventuring while he sleeps, leaving him physically exhausted when he's awake.
4. When Spider-Man, curious as to why he's suddenly tired all the time, discovers the truth, he rejects the symbiont.
5. The symbiont slithers off, only to find a new host (Eddie Brock) that also happens to hate Spider-Man.  The two become known as "Venom".

Now we get to the interesting (whiny) part: why Eddie Brock hates Spider-Man.  A man named Emil Gragg had "confessed" to him that he (meaning Gragg) was a serial-killing supervillian known as Sin-Eater.  Brock, a journalist, is so eager to get a scoop that he forgets one of the cardinal rules of his craft: always check your facts.  In this instance, the only thing Gragg is guilty of is being a compulsive liar.  When Spider-Man catches the real Sin-Eater, Brock's career takes a nosedive.  No matter how unheroic Spider-Man's other choices may have been, such as letting Sin-Eater continue his killing spree (which would have revealed Brock's shoddy journalism anyway) or killing Sin-Eater, his main concern should have been saving Brock from his own error.  And that, for pure whininess (which, believe it or not, really is a word), is hard to top.