Sorry, I can't attend the reunion.

I apologize for not being able to attend the party, as follows:

1. Busy at work: You can tell your classmates that they are busy at present and don't have enough time to attend the party.

2. Physical discomfort: For example, if you are sick recently or have other health problems, you can tell your classmates that you can't attend the party for the time being.

3. Family reasons: For example, if important family events are about to happen, such as weddings, newborn babies or other major family events, you can tell your classmates that they need to stay at home to deal with these things.