GaAtty
First you try to have a civil conference with the teacher and explain why he carries it and that she should not call attention to it again because it embarrasses him, and it is illegal. (Of course, if she didn't know that before she said it, that makes a lot of difference.) If you are past the civil conference stage, then you should inform the school IN WRITING that he has the disability and request that the school start steps for him to have either an IEP (Individualized Education Plan) or a Section 504 Plan under the Rehabilitiation Act. Either one will result in a meeting at which you and his teachers will be present (if the school does it correctly). The purpose of both of these plans is to provide accommodations for his disability, and the plan will be in writing and each teacher should have a copy. His disability is obviously the diabetes. Under the Rehabilitation Act of 1974, Section 504, an entity receiving federal funding cannot discriminate against an individual with a disability (I assume that your child goes to a public school). The Section 504 plan should include things such as that the teachers will not call attention to his medical things. Perhaps it could include a particular place that he could leave them. The IEP could include the same things. An IEP team is a group created under the Individuals with Disabilities Education Act. The team includes various individuals, including the parent. An IEP can be for any student in grades up through high school graduation. With you present, the IEP team should develop ways to prevent this situation from happening in the future. A meeting of either the IEP team or 504 Student Support Team (SST Team) should be held every year so that the new teachers will know his needs. A SST 504 is simpler, and will be adequate for him, if the school prefers to do that. However, if the school wants to do an IEP, that will be OK for him, also. He will need a current written physician's diagnosis, preferably one that includes a statement of how often he needs to test, etc.
Of course this is a civil rights violation, but it is far too small to take any action on. Discrimination based on disability is a violation of this child's rights under the Americans with Disabilities Act (ADA); the Rehabilitation Act, Section 504; the Individuals With Disabilties Education Act (IDEA); and it is an equal protection violation of the 14th Amendment to the Constitution of the United States. Most states also have an equal protection provision for citizens in their state constitution.