Is it permissible for me to say: "Girls are like germs or microbes because they mix with men," or "This girl is like germs, so beware of her"?

Indeed, clarifying the danger of women's ostentatious display (tabarruj) and its negative impact is true. However, the phrase "woman is a devil" is abhorrent and reprehensible, and it might be misunderstood to mean something other than what is intended. It is more appropriate to express this using what is stated in the texts, such as the hadith: "Woman is 'awrah (nakedness/private parts), and when she goes out, Satan beautifies her in the eyes of men," and "Indeed, a woman approaches in the image of a devil and departs in the image of a devil." This means she resembles the devil in temptation and arousal of desire. From this, it is inferred that a woman should not go out among men except out of necessity, and that one should lower their gaze from her.