I would consider the English "W*nker" suggested above to be potentially quite crude! The meaning varies a bit with context, accent, and intensity.
So, I recommend foreign languages.
I can't in good conscience list these uncensored, but maybe offer some clues. Hmmm..
From our friends in Italy (that's a hint so you can use a translator to fill out the complete spelling for these colorful terms).
As DWalt suggested above, context, pronunciation, and geography (!) can have a big effect on their true meaning. My "Raggazzi" used these all the time in mixed company. When used with a soft casual tone nobody nearby seemed particularly offended or shocked. Ramp it up a bit and add a hand gesture, though, and things get spicy! In fact, hand gestures change everything.
So, these are the classics:
"V*f*nc*lo", or it's shortened "F*nc*lo", or "C*zz*"…
A few phrases are good, too: "Chi c*zzo credi di assere" is a lovely saying.
"S*cchia" is good when accompanied by a hand gesture (no not that one!). Put an accent on the hard consonant.
In fact, my "Raggazzi" often tried to trick me into saying things when I occasionally needed linguistic assistance. (The following is not profanity, but might create some laughs, or get you in trouble with the wifey) "Hey Jim, tell that girl "Fa caldo qui, o sei tu?"
Of course, our German friends are masters.
Start with "Sch**s"
It has multiple meanings, depending on context.
The nice thing is, with a practiced pronunciation, they can be either kinda cute or very edgy.