When I wore a Shoei helmet I’d have three ridges in my hair when I took it off. With the Arai, I have one. It’s worse with short hair (which is how I prefer to wear my hair) than with longer hair. So when I get to work I head straight for the restroom and dampen my hair at the sink. I muss it up and brush it (a comb doesn’t work as well). Works well enough.
So how do you deal with helmet head?
Thanks to genetics and a very low cut hairstyle, that’s one thing I don’t have to worry about!
I shave my head, so I can’t suggest anything from personal experience. However, I have seen helmet liner/do-rag type things that, while they’ll still squash your hair, will at least do it uniformly.
I don’t actually worry about it. Then again I work in a pretty easy going office.
Back when my hair was long it helped tame it, it usually wants to stick out on the sides and back.
Now with short hair it’s not a big deal.
A lot of riders carry a hat or cap to wear when the helmet is off.
This what I do. I try to wash it the night before and put gel in it. If I shower in the AM and the hair is wet or damp when I put the helmet on, it is unfixable. With dry hair and gel a little water puts almost anything back in place (I’ve found the shorter the hair the better).
Today was funny as my hair looked a little funky when I woke up (probably a damp brush would have fixed), but since I was bringing the bike I decided to not wet it and wait til work. When I got in, I found the helmet had “fixed” my hair, and it looked a lot better even w/out damp brush.
Shoei RF-1000 for the record.
You can always get a “hairmet”, like JD on Scrubs. It keeps your hair perfect.
Yup. I keep one baseball hat in one of the hard saddle bags. I can wear them at work, which helps. 
I keep a comb in my jacket pocket, that works good enough for me. I’ve heard some riders like to wear those silk do-rags like the ones caveman mentioned.