I think one is entitled to reconsider one's friendship with people if they are the "smash the wedding cake into the other person's face" type, and the guest is not, just as one might reconsider one's friendship for any other reason. "Eww, I didn't know John and Jane were that type of people to hold food fights in front of a captive audience," is s valid reason to back off a friendship, just as John and Jane can back off their friendship with a guest who doesn't get a bellylaugh out of their shenanigans.
People can be incompatible without one or the other being wrong about anything, and something like this is, as the poem says, "a small thing, but indicative".
I agree with WillyNilly, who put it very well - if the act is not of mutual consent, but of one person humiliating someone they have just sworn to love and cherish, it is a terrible thing to have to witness as a guest.