Mrsjones, maybe you meant to submit this under Tagalog and not English.

Bakit hindi instagram? = Why not instagram? (Why use something else and not instagram?)

Bakit hindi ka mag-instagram? = Why not instagram? (Why not join/use instagram?)  

a: why don't you create an instagram account?
a: bakit hindi ka mag-create ng instagram account?

b: i don't want to, not one more password to keep.  
b: ayoko, kasi isa na namang password ‘yun para tandaan = I don’t want to because that would be another password to remember.  – this is how we would say it.

a: come on, just create it.
a: sige na, mag-create ka lang. OR  sige na, i-create mo lang.

b: i don't want to.

b: ayoko

b: ayoko nga e = I said, I don’t want to

a: come on, just instagram.

a: sige na, instagram lang

b: stop pestering me!

b: tigilan mo ang pangungulit sa akin!   

b: huwag mo nga akong kulitin! = please don’t pester me! – this would sound more natural