#1. Not purchasing/mining when it first started.
#2. Overbought by 7 BTC when index was around $750. Going to sleep, waking up at $650 index. Not wanting to take a loss, and holding. It has not come back up since

#3. Sent about $10k worth of coins to a dormant address by accident. Panicked for about 8 hours thinking I sent them to an old client, or random person. Luckily they showed up in an account I owned. Now that I own a Trezor, almost impossible to make that mistake ever again.