Almost being able to masturbate to something. Being in a semi-turned on state. You want to be turned on by what's in front of you but it's not quite hot enough to give you a good hard on, like a non lesbian porno.
Roger: Hey Charlie, what did you think of that new movie Jennifer's Body?
Charlie: Total garbage man. You don't even see Megan Fox nude. I could only halfsturbate to any of the good scenes where she was almost nude.