[Every regret not messing?]

Yup! I've held it before then changed my mind. Every time I go in the toilet I think about how great that would have felt in a diaper or some panties. 

 

[How to poop]

Hold it in for as long as possible until you're really desperate then put a diaper on and release. Alternatively, you could use laxatives or suppositories to force a mess

[Kinda Personal...]

Messing your diaper is fine, even for females. Just don't stay in it for too long (maybe an hour tops) and for a female, make sure the mess doesn't move up the front too much near the vaginal area. Extra cream and powder can help make a 'barrier' between the mess and vagina, to help prevent infection

[Who likes pooping in their underwear?]

I love to poop my panties. Messing diapers is fun but it just feels extra naughty going in a pair of panties hehe.

[Why do some AB/DLs want to simulate a poop in their diapers? Isn't it easier to just do it and then get tho full experience of being a little poopy girl/boy?]

I prefer to actually mess mine, feels more natural and naughty. But for people who don't like the smell or cleanup, I understand them wanting to use substitutes. Plus, sometimes you can't mess when you want too