Different inflectional forms of くれる

Question

In what situations would someone use one of the following forms over the others when requesting the action やる?

1. やってくれる?
2. やってくれない?
3. やってくれ
4. やって(ください)

My assumption is that the first two would translate more along the lines of "Could you do it?" while the last two would translate to "Please do it." (Am I correct?) But between (1) and (2) and between (3) and (4), what are the differences?

Answer 1

Not 'can', but 'will'.

1. Would you do it (for me)? (Spoken by a girlfriend, close female relation)
2. Won't you do it (for me)? (Spoken by friends, classmates, co-workers)
3. Please do it [gruff]. (Spoken by authority figures)
4. Please do it [straight]. (Same as 3, with a slight attempt to not sound so gruff)

There is no great substantive difference in meaning between (1) and (2). (1) just sounds more cutesy. (3) sounds bossy or angry, while (4) just sounds 'direct'.

For (4), you wrote やって（ください）. If we are assuming that only やって is uttered, it is yet more direct and aggressive than やってくれ, but not as much so as やれ.