I don't really think they were trying to be funny

Copied verbatim from the text of the talk about the upcoming dance by the head of a school that I don't work at:

Please abide by the following dancing guidelines: (a) consensual (b) vertical (c) nothing over sexualized.

I don't really like to dance, so my dancing is rarely consensual (grudging is a better word), but the intriguing one is definitely 'vertical.' It makes you really want to know what happened at the last dance.