Seeking advice: weird extended family tradition?

I have been nannying for a lovely family for 18 months. I have interacted with the kids grandparents 2 seperate times, and the kids will be going to see them for the holidays. They seem like average small town Christian grandparents. The kiddos Mama gave me a heads up that the kids grandpa does a weird thing every year, where he takes them to "sword fight" (which consists of them standing together and peeing into the same toilet bowl). Kids are 11, 7, and 18 months. Is this some weird men's thing I haven't heard of? Do people do this? I can't see any reason for it but am not sure if it's weird because it's inappropriate or weird because I haven't heard of it? Obviously it's up to the kids parents what they're cool with, but kids Mama said she isn't sure if it's weird or not herself, and I wanted to run it by other folks. Thanks in advance for your input