It’s such a commonplace today it would be easy to take it as just another vulgarity.
But it could be taken as an ironic metaphorical taunt “go right ahead and pleasure yourself obscenely.” A very light treatment is the key. Paul didn’t fill the whole bible with gutter level retorts either. But as the Proverbs say, sometimes the time is right to answer a fool on his level, to call him out.
I agree with her sign. I’d just have to be asking forgiveness for the vulgarity. :-)