I've tried to research this topic a lot and since I'm not a native English speaker, I can't tell whether it sounds "right" or not when you flap these words. I've found some examples on youtube of seemingly native people who flap it. Correct me if I'm wrong but I think Avril Lavigne flaps "didn't" in her song "Tomorrow You Didn't".
Somebody singing it in a song though, may not mean it is "okay" to flap didn't (or wouldn't, couldn't, etc). Is it common?
Also, I think some people differentiate "written" and "ridden" by flapping the latter. On the other hand, some people don't. Which is more common?
Thinking about this has given me multiple headaches over the last few days so if you have any input I'd be very thankful. To a native speaker, does flapping these words make them sound strange or not?
For reference: Wikipedia - Flapping