1. most inappropriate in timing; occurring at the worst possible moment
Usage: superlative form of untimely

Examples

• The power outage came at the untimeliest moment during the presentation.
• Her phone rang at the untimeliest time during the wedding ceremony.
• The storm struck at the untimeliest hour of their camping trip.
• His joke came at the untimeliest point in the serious discussion.
• The delivery arrived at the untimeliest moment when we were leaving.
• The news broke at the untimeliest time for the campaign.