There are many state tripoints, but a) I only care about the ones around Pennsylvania and California (seven) and b) even of those seven, four of them are in water.
The ones that are in the water are:
Of the remaining three, I've made it to two of them:
Since I've been to the two tripoints including PA and MD, that means I've been to both ends of the Mason-Dixon line. According to noted geography expert my wife, that has only been accomplished by two other people in history: Mason, and Dixon. So now you have to call it the Mason-Dixon-MDK10 line. (I'm a humble man so I volunteer to make my name last.)
[Added later due to coolness] Austria-Slovakia-Hungary