Is he a bodybuilder or professional powerlifter? If so, does he keep food in the "murse" (man purse)?
That, I could understand. Even Ronnie Coleman (Mr. Olympia, duh!) regularly walks around with a fanny pack containing protein bars/pills/etc.
If, however, he does not qualify for the above example, he indeed should stop. Tell him you think men who don't wear fanny packs are sexy. Or, perhaps, tell him he is burning extra calories needlessly by carrying the added weight of the groin-bivouac!
I'm sorry for that one.