PO: suggests a new feature to be implemented

My dev colleague almost always responds no matter what the feature is: 'it's simple to do'

Me: 'Dying inside'

We have a standard response: ’No’.

Maybe that colleague expected that

"It's simple, but it takes time."

It's just so irritating that he has to say that for almost everything. It gives a wrong image about it, because often it's easy to see the things aren't simple. And you gain nothing by saying that too easy. It just sets you up for a big failure when reality starts hitting

Your colleague can do it then if it's so simple

Let him do it then!