@Doomroar - It's not like she's just trying to awkwardly ram the corner point in, but instead just stimulating the labia. It can actually make for good foreplay. When my GF and I were both virgins, sexual encounters would usually start with her riding my knee, much like this girl is using desk / box corners.
Not trying to humblebrag about sex, just trying to note that grinding hard objects like that can be pleasurable.