Cool like a banana

I've just got back from Tanzania and learnt some basic Swahili along the way. My favourite phrase has to be 'Poa kichizi kama ndizi' or as it would be in English, 'cool like a banana'. While climbing Kilimanjaro this could be used in response to questions about how we were and the guides enjoyed getting us all to try and remember it and say it correctly. It took our minds off the trek for a while anyway. I was trying to think of how we might translate it into English. The obvious phrase seems to be 'Cool as a cucumber'. But if someone is cool as a cucumber they are a little distant, aloof, removed. I wouldn't say it's a cool thing to be. And nor would I reply to the, How's it going? with 'Cool as a cucumber'. But, even though it's not an English phrase I could happily say, 'Cool like a banana'. Bananas are just more fun than cucumbers. We associate them with sunshine, slapstick humour, fun desserts - banana split, Bananaman. But cucumbers? They're rather cold, tasteless, salad vegetables. The more I compare the two phrases the more different they become. I can't think right now of a more appropriate English translation for, Poa kichizi kama ndizi, so for now I'll stick with the literal, Cool like a banana.