When the panties/bikini can't contain all the dick. Seems to work fine over all so I'm releasing it. Seems to work for most garment types that would allow for showing some trunk. When it does fail it seems to just make a bulge which is fine with me.

Trigger word: futa_overflow

Helpful words: panties, bikini, pants, loincloth.

BTW, get in comments section and maybe you too could get your idea made into a LORA.