I suspect that very few people would complain about a parent with a small child that walks back through line saying "I'm sorry. Potty break.". The issue people have are with....
- Blatant line cutters who claim to have someone up front, but don't.
- Those who are busy doing other things while their family members get in line, but feel 'entitled' to join them when they are finished doing whatever it is that delayed them from getting in line.