Praise be to Allah.
If the product has symbols of the disbelievers, such as crosses, on it or there are written on it words that constitute disbelief, such as mockery of Allah, may He be exalted, then it is not permissible to sell it or to buy it, because that comes under the heading of propagating disbelief and helping the disbelievers to spread it. Moreover, it is obligatory to denounce that in the strongest terms, and at least to boycott it. This has been explained previously in several answers on our website. See the answers to questions no. 126602, 47060 and 112052.
But if the product is free of any symbols or words of disbelief, and this was only written in the description, then what appears to be the case is that this product should also be boycotted, as a rebuke to the one who wrote these mocking words, and he should also be denounced as much as possible.
It should be made clear to him that his mockery has kept people from buying his product, in the hope that he will remove it, for these people worship material gain and strive for it by all means, but sometimes resentment and ill feelings overpower them, so they do such things as this, or they try to entice atheists to buy their products.
Allah has not caused His slaves to have any need of people such as this disbeliever. Whoever looks will find a similar product or something better than it with another vendor. The interests of supporting and defending Islam and denouncing this grave evil take precedence over any other interests.
And Allah knows best.