Head Hit
With the headhit we're slowly treading into territory only really useful for rollouts, trick jumps, and lucio surf. Headhits aim to achieve the advantages of oneticks without the disadvantage of losing speed. It works by hitting your head into a ceiling.
Execution
Head hits require a ceiling directly over your jump off point. All you have to do to perform a headhit is to skim while having a ceiling directly above your head.
The skim acts as your normal jump, however because there is a ceiling above your head, you're going to hit your head on it, cancelling all your upwards momentum. This means you get the same downwards trajectory as with a onetick.
Pros and Cons
Executing a skim instead of the wallride you do on oneticks allows you to build speed while still lowering your overall height. This is the major advantage headhits have over oneticks. This extra speed also leads to its major disadvantage. If your next jump spot is too close the wallride cooldown will still be active when you get there. You therefore have to choose between oneticks and headhits on a per situation basis.
Tips
The jump for a headhit is not limited to only skims. You can do any jump you want, as long as a ceiling is above your head at the point of inputting the wall jump.