Bacteria produce diverse toxins to eliminate their competitors; however, some of these toxins provoke retaliation. Gonzalez et al. now show that an Escherichia coli strain, which produces a DNA-damaging toxin, incurs a fitness cost in one-on-one competitions, as DNA damage upregulates toxin production in the competitor. Other toxins that do not affect DNA integrity have no ‘provocative’ effect. Interestingly, the provoking strain can have a fitness benefit if it faces more than one competitor by increasing their aggression against each other. The benefit occurs if the provoking strain is spatially shielded from or resistant to the toxins of the competitors, both scenarios that are likely to be found in the microbiota or biofilms.