Stop LastPass filling out a form

Two conditions have to be met:

1. The form (not the element) needs to have autocomplete="off" attribute
2. Lastpass user needs to have this option enabled:
   • (old) Settings > Advanced > Allow pages to disable autofill
   • (new) Account Options > Extension Preferences > Advanced > Respect AutoComplete=off: allow websites to disable Autofill

So this depends on both user and the developer.

Adding

data-lpignore="true"

to an input field disabled the grey LastPass [...] box for me.

Sourced from LastPass.com