I didn't feel anything. Here is why...
1. It is current passing through tissue that causes pain, not the voltage.
2. The DC current threshold for pain is about 5mA.
3. Skin resistance is what determines the current for a given voltage. In this case 12VDC.
4. Skin resistance is not constant and can vary from ~1K ohms to several
100K ohms. Usually dry non-abraded skin is in the range of ~50K ohms to ~100K ohms and higher. Sweaty hands can be lower.
5. The current that will flow with 12V and 50K ohms is I=12V/50K=0.2mA and that is ~1/20th the threshold for pain.
7. The bottom line is that unless your hands have low resistance, <5K ohms, no pain will be felt. If you have an open cut or sore on your fingers you probably will. If you have wet hands, you may feel pain. If you have felt a shock from 12VDC, then you have unusually low resistance skin, which is not normal.
Working as an engineer in a lab, for 38 years, we considered 50VDC to be the threshold for getting more than a tingle and had to guard any exposed voltages greater than that. From OSHA - "live parts of electric equipment operating at 50 volts or more shall be guarded against accidental contact".
Lastly, have you ever seen a warning sign under the hood of a vehicle that says Warning Shock Hazard?