Positive or negative what? Conversation or for the spell?
If you are talking for the spell then I would have to say no, if anything it may help you concentrate more on that person because you have a more resent encounter with them. Since it is your energy behind the spell you need to do what you can to make your focus strong to give it a better chance of working. I say better chance because you can still only go so far (in my opinion and experience) on someone else spell. I believe that the ones that you write (create) will always be stronger then what someone else has created because you put your energy into creating the spell.
Anyways hope this helps, Blessed Be.