Tomato-My first tomato grow in a tent. I have my...

Looks like a calcium deficiency. The german word is close to budrot (Blütenendfäule = budendrot), but it is not dangerous for other plants. The lack of calcium just give the cell a problem that they can not handle. You could even harvest that tomatoe and cut away the bad part and try it. If it tastes fine - enjoy. If not it is still not a problem for your body in any way. When the green tomatoes get enough calcium, they will become completly red.