Here we have 'offends' with the singular agreement, and in the very same sentence the plural verb 'are' (contracted to 're).
We also have a pronoun 'they' which can be used for both singular and plural referents, at least in colloquial usage and probably in many formal registers too. However, it's prescriptively plural, and this can affect its usage in funny ways. For instance, it's unusual to hear 'themself' and spellcheckers don't allow it, even when referring to a singular antecedent in a sentence like 'a student has left their file here. They'll be kicking themselves later'.
It's impossible (for me, at least) to refer to a band as 'it'. This is a bit surprising seeing as a band can be singular, as noted above. I don't know the reason for this. But it means that we have to use 'they' and we have a singular verb 'offends' in the tweet above, followed by the frequently singular 'they', followed by the plural 'are', all of which should be one or the other. But because at no point is there a mismatch between two adjacent items, the long distance mismatch comes out just about ok. 'They' mediates between the singular and plural verbs and both are deceived into thinking they're in the right number form.