Originally Posted by Roforot
I wouldn't necessarily call a foot fault, but I might suggest to him if he steps in 4-5" into the court, then he should lose 4-5" of the service box
If he doesn't like that idea then he should keep his feet behind the line.
I like that idea! Call the serves out by the same distance he'e f-f'ing. That might make the point clearer, tell him your reconfiguring the geometry of the court as a compensation, so as to equalize the playing field, as it were.