Well as the title says pick the animal you would least want to be attacked by and your reasoning.

I say a tiger. This is because they are huge cats, and you cannot get away from them. They swim, climb (trees and cliffs), and can pounce 15ft. Not to mention they weigh 600 pounds and have huge claws and teeth. Also they always bite for the neck, and if your human that pretty much means decapitation or damn near.

A 'Mewtwo'.

Can they be extinct animals?

Well I wouldn't want to be attacked by a bear.
They are pretty strong and can run sorta fast.Faster than my atleast and I have a very slim chance of staying alive if the bear wants me dead.

A saltwater crocodile in open water would suck ass.

- ♫.i.b.y.v.n.t.h.♫

A howler monkey riding a wolverine.

why WOULD you want to be attacked by an animal

http://www.cellscience.com/aids.jpg

AIDS.

-N-

I wouldn't want to be attacked by any animal...
Oh, and btw, AIDS is the result of a virus, not an animal.

TRUE.

I was thinking more along the lines of what I would least like to be attacked by.

AIDS still sucks.

Back on track... I would hate to be hunted down and killed by a polar bear.

-N-

Tyrannosaurus mother fucking rex
Bitches are huge and shit.
"Although other theropods rivaled or exceeded T. rex in size, it was the largest known tyrannosaurid and one of the largest known land predators, measuring over 13 metres (43 feet) in length and up to 7.5 tons in weight."

I wouldn't want to get attacked by a Megalodon either
"The best-educated estimates of this creature's maximum size range from 12 to 16 m (40 to 52 ft) "

"From the size of this shark, its weight is estimated as high as 60 tons, though 20 to 30 tons was more likely. Assuming similar metabolic-weight ratios as the great white shark, it is estimated that a large megalodon would need to eat about one-fiftieth of its weight of food on average per day."