Anyone ever ran into this? I turn the hot water knob on and then just barely turn the cold water knob on and the water goes (all cold instantly).
This behavior is specific to your plumbing. It’s not supposed to work like that but maybe you have some pressure issues on the hot water side, maybe an issue with the hot water tank (IANAP).
How old is your plumbing fixture? Sounds like a malfunctioning pressure balance spool.
You could install one of the new single handle auto-mixing valves…
Anecdotal:
Before we updated our bathroom, with the new (code required) pressure balance single control knob, we had the same issue. A couple sections of the cold water pipes that ran along the basement ceiling were larger diameter lead, and the hot water pipes were smaller diameter copper (standard size today).
Because of the unbalanced pressure between the two pipes, only a small amount of hot water was needed to take a hot shower.
Before you ask, the plumber* said the lead pipes were safe now as the buildup inside would keep the water away from the lead.
*Old family friend in the business for 30+ years - take it for what its worth.