What is the ruling on using words like "bull" or "oxen" to describe a person or people with the intent that they are large-bodied and strong, knowing that the listener may perceive these words as offensive, and is this considered backbiting (ghibah)?

Gheebah (backbiting) is your mentioning of your brother with what he dislikes, whether it pertains to his body, his religion, his worldly affairs, his self, his physical appearance, his moral character, his wealth, his child, his father, his spouse, his servant, his slave, his turban, his garment, his gait, his movement, his cheerfulness, his flippancy, his frowning, his pleasantness, or anything else related to him. This applies whether you mention it with your words, or in writing, or by hinting, or by pointing to him with your eye, or your hand, or your head, and so on. Its definition is mentioning a Muslim with what he dislikes.