About Pre-Opening (backside of hand?)

[diegoC]

I'm re-reading 'How to make girls chase' and i found this

One common way of pre-opening a girl is to position yourself next to her, then lightly tap her on the arm with the backside of your hand …

The thing is, I remember reading somewhere here (surely) that we should not pre-open using the back of our hands as it may feel cold.

Any thoughts on this?
Thanks!