I don't think most people who asked is my dog a teacup are mean-spirited,rude, or trying to cause the yorkie breed harm...just possibly curious. If I have the time I usually tell them there are no "teacup" yorkies. I explain the AKC standard weight limits but also say there are so many that fall out of that range. I usually use the poodle as an example of three size varieties that are acceptable but there are no variations like that with yorkie. Most of the time I take this as not only an opportunity to share what I know about my babies but an opportunity to show kindness to someone.
If you are rude or sharp with someone who is ignorant on any subject, they won't really remember anything other than how you treated them. There was a time when researching the yorkie I asked questions that were probably considered lame too
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I have learned to hold my tongue after years of cutting people down with it. I'm still a work in progress!! I just wake up every morning grateful for another day and use the day as an opportunity to show kindness to whoever I come into contact with.