Firstly, very few people are actually vegan, that is to say: Not Using products that are derived from animals.
If you have ever used any of these products you are not a vegan.
All of these products come from cattle
From the top!
Brain: Anti-aging cream, Medicines
Hooves/Horns: Adhesives, plastics, pet food, plant food, photo film, shampoo and conditioner, lamination, wallpaper, plywood
Blood: Posta, imitation eggs, cake mixes, dyes and inks, adhesives, minerals, medicines, lab research materials
Bones: Refined sugar, charcoal, fertilizer, glass
Internal organs: Instrumental strings, tennis racquet string, hormones, enzymes, vitamins and other medical materials
Milk: Adhesives, plastics, cosmetics, medicines
Hair: air filters, brushes, felt, insulation, plaster, textiles
Skin: Gelatin, flavorings, sheetrock, wallpaper, adhesives, medicines, candies and confectionary
Manure: fertilizer, nitrogen, phosphorous
Fat: Chewing gum, candles, detergents, fabric softener, deoderant, shaving cream, perfume, petfood, cosmetics, creams and lotions, crayons, paint, oils and lubraicants, biodiesel, plastics, waterproofing agents, cement, chalk, explosives, fireworks, matches, fertilizer, antifreeze, insulation, linoleum, rubber, textiles, medicines
Secondly in response to Gibby in order of appearance:
1. I doubt anyone worth answering would ask such a subjective question because they would receive and equally subjective answer.
2. Sounds like a vague dodge attempt to me, not convincing.
3 Why do I eat meat?
Because I can, not in terms of choice, but because it is a readily abundant source of food that my body was made to eat.
Yes that's right, the human body was made to eat meat, it is evidence enough that we physically can eat and digest meat to a successful degree to prove that our body can and arguably should eat meat.
One of the problems with some(possibly most) vegans is that they see discussing their views as an "argument" when it is not, it is discussion. Gibby gives the advice to not be on the defensive, which in terms of an argument logically means you are on the offensive (preachy possibly), this attitude only helps fuel peoples general dislike of vegans for their percievedly contemptuous attitude.
As for AndyBa's answer "For the same reason you don't eat people and wear their skin", this only illustrates that you cannot draw a distinction between lower order animals (cattle for their leather and meat) and higher order animals (US!). This naive attitude does not help your agenda at all as any sane person recognizes that human life far outweighs that of animal life, making your point completely moot.