It can be either a collision issue or the clothing doesn't fit properly into your model. To fix the first, go to Physics tab inside the clothing item and increase the collision radius. To fix the second, go to Adjustments tab inside the clothing item an increase surface offset.
It is also common for nipples (just the nipples and not the entire breast) to poke out of clothing. To fix it use the following plugin.
Credits: Character: 'Ellie' by JackyCracky, 'Shirt Base v2' by VL_13, 'Torn Jeans Shorts' by PetaZwerga Credits: Character: 'Ellie' by JackyCracky, panty by maru01 Eliminate Nipple & Pubic Hair Clipping This session/scene/person plugin...
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Edit: For more complex vertices and geometry editing, use this one.
Clothing Editor This is a plugin that aims to provide a bit finer control to the clothing creation process. Main features include: 1. Visualization of clothing/skin meshes of base/morphed/drawn position. 2. Full/partial rewraps 3. base mesh...
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