I find that do-it works well for voice scratch sound effects. Say it in a lowish voice, two or three times in rapid succession. Make sure to, in the course of a single "do-it", have your voice go from higher in pitch, to lower, then back to higher. The requisite hand motion helps to visualize what the turntable would be doing in order to create this type of effect.

"Do-it do-it do-it". Yeah. Word. Peace.

Also, for people like me prone to conversational typos (speakos? talkos?), the vocalized turntable makes a great save for when you've just mangled a word beyond recognition while trying to just speak the goddamn thing. Just scratch it around a bit, don't leave out the hand motion or people will think you're really nuts (as opposed to just slightly odd) and boom, you're back on track with the conversation.

The pronounciation I prefer is:

"vrp a vrp a vrrrrp," as pioneered by JerkCity.

Variants of this, such as "wikka" and "jikkie jikkie jikkie" also make for a good effect. But there just ain't nothin' like a good old vrp.

I've done this a fair bit since I bought Rahzel's album MTM 2000 or Make The Music 2000. Rahzel is the biggest human beat box around these days. I know of an old school human beat box called Darren Robinson but I haven't heard his shit, so I don't know if he used to scratch vocally.

It's really not that strange of a habit as far as I know, considering a few recent top 100 examples:

Slim Shady's vocal turntable - "Hi my name is tKEtKE Slim Shady"; and

Afroman's Because I Got High - "buk bukka buka BUKAW!" (slightly amusing how the last one sounds like a chicken)

Some things I always find it easy to scratch are anything starting with 'R' (probably because I learnt from going "Rah-re-Rah-ra-re-re-Rahzel") and my rap name Chur-Ch-Chur-ch-chka-chka-Churd-Tzu.

Last time I was jamming and DJ Freezone wouldn't let me use his turntables so I used the mic instead. Everyone thought it was kind of cool, but the ones who appreciated it most were stoned.