I have seen this twice now, so would like some help considering the options.
1. Honk the horn. The problem with this is that it will be taken as encouragement by the one taking the selfie. If it wasn't a good picture, then why would they honk?
2. Ram his car with yours to express your displeasure. This has obvious problems.
3. Go stand in front of his car and do your daily Tai Chi practice.