I give out stickers to kids at elementary school. We play karuta nearly every week, and when the kids have taken five cards, I allow them to choose one sticker from a stash that I accumulate whenever I go to Tokyo or happen to see cool stickers.
When I was in Australia, we passed a dollar store, so I stocked up on cool Aussie stickers. I got a bunch of flags and antipodean animals. They also had a big sheet filled with bugs, one with ladybugs and another with beetles.
Some of the boys liked these stickers, but I still haven’t given them all away. A month or so ago, a girl was trying to choose her sticker and I said, “How about a bug, mam?” 「虫はいかがでしょうか。」, purposely speaking a little over-politely to be funny. She replied in kind speaking slowly, “No bugs, thank you.” 「虫は、いいです。」
No one likes bugs. Except, of course, these crazy kids in Japan, but they’re mostly the elementary school kids…and the few junior high kids who still like them…and become adults who really like them.
So, no, bugs are not nice, good or cool. I’d rather have very little to do with them, thank you very much.
This use of いいですis the often overlooked refusal of something. Think about this conversation for a second:
A: Would you like anything else to eat?
B: No, thank you.
In English, we incorporate “thank you” into our refusals. I can’t tell you how many times my “No, thank you”s have been misconstrued as “Thank you? Well, here ya go!” (Perhaps because I mumble?) In Japanese, similarly, they incorporate a “good” word into a phrase of refusal – いい.
To make it clearer, you can attach a もう to the front of your いいです, implying that “(whatever you) already (have is) okay.” Okay might be the closest translation. So here are your phrases:
（もう）いいです。
（もう）けっこうです。
The second being a more polite version of the first. I think けっこう might be slightly easier to understand coming from a non-native speaker who, like myself, is probably messing up the intonation of the phrase.
Here’s a conversation I had on Wednesday for further reinforcement:
Konbini lady: 袋はいりますか。
Me: けっこうです。
K: いいですか。
You copy? In English it looks something like this:
K: Do you need a bag?
M: No, thank you.
K: You’re okay (without a bag)?
The lady wasn’t asking me if I was good or if I thought bags were nice or something, she was asking me if I was okay without a bag. An easy way to differentiate this usage of いいです from others is that this one will hardly ever, perhaps never, have anything in front of it. The other usage you will see constructed like this: 〜がいいです, with が directly expressing the subject of いい.
Robin wins again this week, with his answer, “somebody offered to put bugs in the girl’s lunch (you wouldn’t do that would you daniel?) and she was politely refusing them.”