Why is it wrong to write 'Servi si nasce, noi lo nacquimo'?
The sentence is an adaptation of Totò's famous sentence
«signori si nasce; e io modestamente lo nacqui»
which could be roughly translated as
«noblemen are such by birth alone; and I, if you allow me to say so, was born such».
Totò's sentence has an exhilarating comic effect in Italian because it is pointlessly pompous, aristocratic; from a grammatical point of view it is correct, but totally inappropriate, extravagant. It is an authentic flash of genius. Grammatically, "lo nacqui" means "I was born that" and, although it is correct, nobody would ever use it in everyday Italian, it would sound ridiculous. As suggested by Charo, you can watch the gag here at minute 8:40.
«servi si nasce, noi lo nacquimo»
is grammatically incorrect because, as pointed out by Josh61, the plural second person simple past of "nascere" is "nascemmo", not "nacquimo". The intentional error has an ironic effect, which is consistent with the meaning of the sentence, which could be roughly translated as
«servants are by birth, and we were beared such» (beared instead of born)