I have tried push back but then the other guy that says "I can do it" gets the ticket handed to him.

Me: we cant do X bceause it has Y and Z implcations for end users

Manager: It fits our brand and we have to do it.

Dev: I can do it and the implications are mitigated by (handwavy explanation)

Maanger: sounds good. (To me) Maybe you can make a (useless) diagram for this featuer that will be realy handy for KT

--Days later--

Feature is delivered and the Y and Z were ethier not mitigated or there was a attempt-ish to mitigate them