Walked in to order a sandwich and cashier( fat gir...

Walked in to order a sandwich and cashier( fat girl) was extremely rude and upset when she noticed I didn't tip her due to her attitude. She turned around and told the sandwich maker something and they all started laughing, which seemed shady and is extremely disrespectful and unprofessional! I'm pretty sure they did something to my food and I walked out and returned my food because I felt like I shouldn't eat this sandwich. Sure enough when I walked in she told the other fat girl that "she's coming back", which consents to me they did infact did something to my food. The manager of this place need to look into those bias and nasty worker's of this place!