The pros never know what they want the forehead poke to be

Itachi uses it on Sasuke to keep his distance and avoid him in a brotherly affectionate way

Sasuke uses it on Sakura because tru luv

Sakura uses it on Sarada to avoid answering her question on Gaiden just like Itachi used to (i won’t even get into the fact that somehow Sakura used in the way it was supposed to be used without ever knowing what it meant)

The first and third time meant nothing but keeping your distance in a friendly way, not romantic. But when Sasuke uses it on Sakura it’s a sign of undying love for her.