Why do I always get a pimple on important days?

Stress is one of the top contributors to breakouts. Important days often equal more stress leading up to the day. Unfortunately, there isn't much to do, but maybe de-stress.

Also, as for one other answer regarding 'hygiene'. While it can play a part in breakouts, it is rarely even a higher contributing factor. I doubt that has anything to do with this case. After all, few people who don't practice proper hygiene would bother to search for the answer to this problem.

stress,,, it's stress

i'm 34 and get them when i feel under the weather or stressed out...

you had not taken proper care for your skin, hence there was a pimple.