Since it generated so many comments and discussion about the origins and use of the phrases, I went googling phrases associated with Tyrannosaurs teeth.
Here’s the search terms and the number of hits (to the nearest thousand).
Tyrannosaurus teeth bananas – 792 000
Tyrannosaurus teeth steak knives – 13 000
Tyrannosaurs teeth railroad spikes – 98 000
Tyrannosaurus teeth bananas steak knives – 8000
Tyrannosaurus teeth bananas railroad spikes – 3.2 million (which must be wrong)
Tyrannosaurus teeth steak knives railroad spikes – 8000
Tyrannosaurus teeth bananas steak knives railroad spikes – 6000
Having explored a bit some of these are probably high – people can discuss Tyrannosaurus relative to other theropod teeth and call those steak-knife like especially, so that could be misleading. However, what is clear is that these are all being used with great regularity. My exploring also revealed a profound lack of qualifiers (e.g. ‘big’, ‘crown’, ‘shaped’, ‘similar to’ etc.) and they generally seemed to be flat comparisons of the “teeth like bananas” kind. This included all manner of less-than-stellar sources like AiG and Yahoo answers, but all the way through to Wikipedia, various museum and university websites and more. In short, these really seem to be pretty ubiquitous on the web.