Haven't read the thread but to me being late (except for good reason of course) is ........
1. Inconsiderate
2. Impolite
3. Sends a message that you don't care enough about the people or the event to be on time
4. Possibly disrespectful
5. Annoying
I'm sure these have all or at lease in part been mentioned by others. Oh well ........ my 2 cents worth.