I want to bring some dried rose petals with me to my upcoming trip to Malaysia just for my own personal use with my hotel bathtub. I'm not sure how much red tape stands in the way between me and this idea. Hopefully since it's not produce I don't have to declare it, or am I mistaken? Surely it's not forbidden to take on the airplane?
As rose petals are not liquid nor a paste and also no security risk, security should not stop you taking them on the plane.
The point where it might go wrong is where you take them into a new country. You can research whether import for personal use is allowed. But as you will only have small amounts the search results may not be clear and just bringing them a small financial risk as long as you declare them on arrival.
Use the red channel, 'I have to declare something', get them out and wait for the officer to tell you yes or no.
On the other hand, Malaysia has a good tradition in having flowers available so it is rather likely that they have rose petals maybe already in the hotel.