Arigato gozaim-arse - Japanese etiquette part 2

I didn`t want to talk about language in this entry, but I`ve just noticed in my dictionary that the negative form of "desu" (be), "ja arimasen", is considered informal. There is a politer version, "de wa arimasen", but in retrospect I`ve never heard a Japanese person say even that. In my experience, they`re more likely to run linguistic circles around trying to re-define a thing, rather than say "it isn`t" or "no" outright. This idea was only fed after I asked Yoshimizu sensei, the music teacher at Kyomachi, if they had a spare trumpet so I could play in the band. My Japanese is limited, but I know she said something along the lines of "Well Chris, you see, the thing is, we have three trumpets at Kyomachi music department, and three trumpet players, and..." and on it went, beyond my understanding. Thankfully, clocking my gradually furrowing brow, Ishibashi sensei intervened with his formidable command of English and gave me the shorter version. Since then I`ve been listening out for Japanese people saying "no" - can`t say I`ve ever heard of it. As a result, I`ve discovered a glaring pronunciation error on my part. Whilst trying to say "no thank you" (iie kekko desu), I`ve been saying "ie koko desu", each "i" and "k" acting as an individual syllable. The "o" is frankly inexcusable. This will explain some of the confused looks I`ve been getting in supermarkets.
"Would you care for a reward card?"
"My house is here."
"?"

Something else I`ve noticed, particularly when teaching the little monkeys at Rinko is that many of the boys try to get me to say words in Japanese that are, and I can tell this just by the looks on their faces, a bit on the rude side. Obviously when the lesson`s over I humour them - their faces light up as I perplexedly fumble around this potential hand grenade of polite society. This week, curiosity got the better of me, and I asked Asanuma sensei to define what they were trying to get me to say - "Azasu". Apparently, it`s an abbreviated form of "arigato gozaimasu" (thankyou very much). So, there`s a bunch of teenage boys cackling in the way that only teenage boys can over the hilarious taboo of the resident English speaker saying a slightly less polite form of thankyou. I love it.