I have actually done this. Not with the dilda but with a different 200mW+ red. It doesnt really hurt. It just burns the sharpie away. it might give a slight sting but nothing major. Its not that bad. You should try...But with a blu-ray thats a whole different story...That hurts...dont even try it lol...
I have done this with my O-Like new style red laser....the black sharpie on the back of the hand behind the thumb. Yeah it hurts, you have to make the sharpie black dot at least 1/4" in diamater to match the same size of the beam (unfocused beam). It hurts immeadiately and I have gotten blistered skin and scabbs from it. That 200mW red laser is really strong. Be careful. You can also shine the beam (again unfocused) on the top of your thigh with blue jeans on and it will get hot pretty fast and the pain will increase. Do this at your own risk as lasers are not toys. Treat them with respect.