If you don't like to be called freight then how about payload?
In every aviation weight (sorry mass) and balance exam, the term payload is used. Whether that payload is passengers or freight is a minor detail.
The term isn't used as a derogatory thing except when they can't get themselves to the gate ontime. I quite happily call myself SLF when I am paxing, it's no big deal. Also I sit in cattle class too.
Oh and isn't that term offensive to you?
Every profession has it's little terms of endearment to those that actually pay us. I am sure computer folk have charming terms for newbies. Oh there's one. What about the medical profession? They have some doozies for patients. Let's not even think what the Police call us.
It does pay to remember that you are in an aviation site. If I wandered into a professional musicians website and got all hissy about being called a punter I am sure I would be told to get lost. Even though I pay to buy their CD's and buy concert tickets.
You would have every right to be upset if the cabin crew and the flight crew addressed you as Self Loading Freight while you are at the airport or on the aircraft. However, this is our down time. Our rest and recreation. It's like a bunch of us are sitting at the bar having a chuckle and a laugh about our work. (us being check in staff, FA's, ATCO's, engineers, loadies and dare I say it, pilots)
Believe me, forklift loaded freight gives us a lot less grief than self loaded freight. It isn't drunk. It's not trying to sneak a smoke in the toilets. It isn't late to the gate other than due traffic. It isn't distracted by the bright coloured shops. It doesn't abuse the staff. It's x-rayed without a murmur. Make absolutely no demands on any one and stays put when strapped in. Doesn't argue about how much it can carry on. Never forgets their passport. Never demands an upgrade. Doesn't use the mobile phone whilst checking in. Never says a smart arse remark about a bomb to the check in staff. The list is long. Now, before you have a massive hiss at me, I have flown both freight AND pax. Both have plusses and minusses.
The one thing I really miss is having pax visit the flight deck.