this is poorly worded, so I'll give my interpretation of what you said and respond. Correct me if I'm wrong
"How weird is it for my friend to be ok when I scratch her head, even enjoying it sometimes (like i did it as a joke)"
I'd have to base my decision off of tihs with your relation with this friend. How close are yall? If you aren't that close then yeah, that'd be weird. Otherwise it's ok i guess? sorry for talking too much