LOL we just found another planetary constant: my mom told me literally the same and she was told it by her mom.
(to which admonition the traditional reply in my family is: "and stay a good catholic, don't engage in intermarriage, don't get run over by a tricycle and don't fall into a letter box!"
By "intermarriage," I assume they meant marrying outside of the faith -- as opposed to, say, marrying someone of another race or another species.
Hey, scot!...just for the record, Rhubarb wrote the above quote, not me...
...however, to your comment, I am not, theoretically, opposed to inter species marriage, and have heard it said that
" ... It doesn't matter when it's Arcturian, baby!"