Board Thread:Wiki Discussion/@comment-34632068-20180117172908/@comment-13682699-20180117235321

What is considered gross usually varies by each person and their preferences.

However, there are ships that take it a step too far and involve socially taboo relationships. For example:

Toriel x Frisk: Pedophilia

Sans x Papyrus: Incest

Such pairings involving those kinds of relationships are very frowned upon by the community and would better suit the definition of "gross" in general.