The policy is ridiculous not because it exists (that's a separate argument imho) but because it's so subjective and worse still it's, as per QF's general MO, very INCONSISTENT in it's application. Plus the fact that it's only for some lounges and not others leads to confusion all around.
To pull an example, sort of, from earlier that it's OK to go SIN-PER but then not PER-ADL (a valid routing) then that seems crazy.
Further, I saw a report that thongs et al were fine in SYD just yesterday (it was 36C or something). So someone is fine in SYD and what if they want to return, or try it again in 2 weeks and rejected?
I've seen some agents standing by the escalators at SYD (by the dress code sign) enforcing it, most times there's nobody.
it all sends a mixed message and it's subjective.
I would note that the "new" (well up for months now) signs (with example pictures) are much more clear and helpful than the initial ones so I feel the policy is clearer, and people can't say they aren't informed.
I've written many times before my personal opinion is that the problem is NOT thongs or singlets or ripped jeans, it's more attitude and hygene that should be policed. Jerks in suits - I've seen my share in the J lounge and perfectly clean and well behaved peeps in shorts, thongs and tees. They worry me less than the smelly boozed up selfish idiot with their feet on chairs or tables (bare or otherwise) that I find offensive.
All that aside.. the policy is there. QF has a right to have a policy in their lounges I feel... but they need to be clear policies that are not so subjective and be consistently applied, or else they may as well not bother IMHO.