In this paper, we investigate how mismatches between biological gender and avatar gender affect interpersonal distance (IPD) in virtual reality (VR). An increasing number of VR experiences and online platforms like Rec Room and VRChat allow users to assume other genders through customized avatars. While the effects of acquaintanceship and gender have been studied with regard to proxemic behavior, the effect of changed genders remains largely unexplored. We conducted a user study (N = 40, friends = 20, strangers = 20) where users played a two-player collaborative game in Rec Room using both male and female avatars. We found that with swapped avatar genders, the preferred distance increased between friends but not between strangers. We discuss how our results can inform researchers and designers in the domain of multi-user VR.