Wolfie, I have had the same experience. I explained to the individual in question that what we were doing was called tefilla b’tzibur and if he wanted to carry on a private conversation, even with G-d, he should take it outside.
And that is the key point. A minyan isn’t just ten guys davening. It’s ten guys davening TOGETHER. If one man’s davening or actions farshster the davening of one of the other mispallelim, the whole minyan, the tzibur is farshtert.
Many folks don’t realize how chamur the inyan of tirchah d’tzibura is. Just to remind everyone, the reason we take out two sifrei torah on Yom Tov (three on Shabbos Chanukah, Rosh Chodesh) is because of tirchah d’tzibura. We actually mevazer and endanger a sefer torah just so the olam shouldn’t have to wait while we roll it from parsha to parsha.
GHJ, As others have have suggested, if you Shokeling is really farshtering someone eles’s davening either tone it down or go to the back of the beis medrash.