In addition to "tell them that you cannot fix bugs that aren't reported" (as covered in recent answers) you need to make reporting a bug as easy as possible. Most non-IT people feel intimidated by the prospect of having to use the ticket system and think it's far too complicated for something they can simply tell someone.

If a colleague starts ranting, show them the ticket system (where to find it) and file the bug together to show them how to do it. If possible, create a template with the most important information you need:

• Name of the app (you won't believe how many people forget that)
• What did they want to do
• What/where did they klick
• What happened instead of the desired behavior (the actual bug)
• Add a screenshot if possible
• Name of the bug reporter for call back

In addition, encourage colleagues to report bugs. Make it clear to them that reporting a bug is good, helpfull and has a positive outcome. Some might feel like betraying you by revealing "mistakes" you made.

In addition to "tell them that you cannot fix bugs that aren't reported" (as covered in recent answers) you need to make reporting a bug as easy as possible. Most non-IT people feel intimidated by the prospect of having to use the ticket system and think it's far too complicated for something they can simply tell someone.

If a colleague starts ranting, show them the ticket system (where to find it) and file the bug together to show them how to do it. If possible, create a template with the most important information you need:

• Name of the app (you won't believe how many people forget that)
• What did they want to do
• What/where did they click
• What happened instead of the desired behavior (the actual bug)
• Add a screenshot if possible
• Name of the bug reporter for call back

In addition, encourage colleagues to report bugs. Make it clear to them that reporting a bug is good, helpfull and has a positive outcome. Some might feel like betraying you by revealing "mistakes" you made.