Most dads wear jeans or trousers every day, but many haven't replaced them since before you were born. If you don't think the guys at work would give him too much of a hard time, think about a pair of durable, well-fitting, US-made pair of Blackbird pants or jeans for Father's Day. This could be the best thing you do for your dad in a long time.
Blackbird Hazlewood Jean in Nep Indigo
Blackbird Hazlewood Jean in Stolen Black
Blackbird Trouser in Black Japanese Twill