Do all guys masturbate?

Look...The large majority of men masturbate. However, there are varying degrees of the male sexual drive. Some men need it more than others. And yes, there are a lot of men that do it, and lie about it. So I really can't tell you whether your friend is a liar, or just not that horny.

if a guy is having sex regularly, it's less likely that he masturbates.

it might be helpful to think of guys attitudes to masturbation as the same a girl's to chocolate ;) the less bored & more attention a guy is getting, the less he feels the need for it.

most girls I know are very prudish about their own masturbation: they still have hang-ups about it being "dirty" or "wrong", which is a shame.

lots of guys masturbate, even the ones that say they don't have done it at 1 point. The only reasons a guy would not masturbate is if its against his religion and he's very strict with it or he had his "little buddy" chopped off and/or had a vasectomy lol
Me, I hardly ever do it so I'm pulsing with sexual pressure that I can use on my girlfriend, I remember a time where I did it 6 times a day! Eventually it goes down I would say I do it 1 or 2 times a week more if its her time of the month.

Of course they do. Lying about is pathetic really or they have to get laid a whole lot. And girls masturbating, why would that be any different from guys doing it? Don't find it odd at all.

all the guys masturbate
or else they die haha

There are two type of guys:
Guys that masturbate and guys that say they don't