I remembered back when I was very young, probably not more than 5, when I developed my shampoo obsessions. I'll never remember exactly what opened my eyes to it, but I do have some memories.
One memory is when I would imagine a bunch of guys - male characters from movies I'd been watching - standing around a bathtub, washing my hair, though I couldn't see myself in the vision, just the guys around me. I'd ask them to stop and there'd be a collective "awwww" followed by one guy asking "just a little bit more?"
Sketchy as hell, I know.
Other images I had involved being kidnapped by someone wanting to wash my hair, or being chased. I thought it was odd that I'd be afraid of someone washing my hair, and nowadays I think it's very weird that that's what I thought a kidnapper would do, rather than rape or kill me, two acts I couldn't even imagine when I was a kid. I didn't know what rape or sex were until I was about 8, and I had no knowledge of sexual pleasure, just the pleasure I imagined I'd get from having my hair washed, and the weird idea that some guy might want to do it to me without me wanting it.
In my own way, I had already begun to conceive notions of rape, consent, and gender roles in acts of pleasure.