need help with coworkers who JUST DONT GET IT!

I work at a resteraunt (so i guess since its not a pet store or anything, its not like they would get fired or anything), but i am very sure that 2 coworkers of mine need a hard lesson in fishkeeping. I overheard them talking ond day about theri tanks, and the conversation is kinda as follows:
(I'm just gonna call them "J" and "E"
J- Yeah my kids and husband got me my tank for my birthday last year (sept 2003)
E- I've had my tank for about a year too
J- My fish are getting so big (holds up hands to represent about 8" or so) my oscar is this big, (...represents 6" or so) my shark is this big (and then rattles on a list of about 6 other fish, and says that the smallest is about 5")
E- yeah i have 2 oscars and a shark (oscars about 12" and a shark about 8")
---Me thinking "WOW! these guys are hardcore! they must have HUGE tanks"... So I intervene
ME- hey guys... sounds like you guys have some nice tanks... especially with oscars... how big are the tanks anyways?
E- 30 gallons
J- 20 gallons
ME- EEK! thats not enough
J- oh really
ME- do your fish swim into the sides HARD sometimes
E- mine do that lots... its funny
ME :mad2 - *MAD*that means they dont have enough room
J- well they are still alive it dost matter
---and the conversation goes like this for a while---

I was thinking you guys can tell me what to tell them to scare them into buying bigger tanks, or taking them back or something? Thanx

LOL! I wish i could gonefishin. but i think im just gonna print out this page: http://www.bestfish.com/tips/102298.html and go over it with them. if that dosnt work... *konk.... drag drag drag drag.... skreetch... click* into the downstairs office they go. for a year or so.

FTR- These woman are not very bright individuals so i wonder if I should blame it on that. one thinks that deep fried tortillia shells are a healthy snack for kids and thinks shes size five 140 lbs (how??? she a foot and some taller than me, much wider, and only 10 lbs heavier???). the other is 27, works as a dishwasher, while her husband hasnt had a job for years (cuz they wanted to try the role reversal thing) and 4 kids on top of that. I hate being judgemental, but i have to be with people like that, i have to find reasoning why they would do certain things

E doesn't cuz her kids broke it a while back, so now she has just an airstone, but J does, and its the same as mine (on the same size tank), its an aquaClear Mini. the only difference between our tanks in hers is ovorstocked, but mine have 4 adult guppies and maybe 12 fry. I keep them together for population control.