I read that due to geometrical constraint, positive carbons in an aryl carbocation exhibit sp^2 hybridization instead of sp^1. The empty p-orbital is forced into a hybridized position via geometrical constraints. This then explains the instability of the carbocation as the positive carbon is attached to a significantly more electronegative carbon. Understanding that carbons with more "s-character" display more electronegative behavior, please clarify the following questions:
1) What is the hybridization of the positive carbon in a vinylic carbocation?
2) Are geometrical constraints present in vinylic carbocations?
3) What makes a vinylic carbocation unstable?