Asking for a friend.

Completely stopped traffic, “Car A” is signalling to go in behind “Car C.” The driver of “Car B” has left a cars length between his car and “Car C.” “Car A” begins to merge between “B” and “C.” The driver of “B” is texting and without looking up pulls forward as “A” is pulling into the gap, rubbing along the side of “Car A.” Who is at fault?