Learn English – n idiom or euphemism for when someone has an average/small penis but knows how to use it

Expending disproportionate effort on trivial matters is sometimes known as bike­shedding, or Parkinson’s Law of Triviality.

Jeff blogged about the phenomenon in the context of it being a problem on Stack Overflow...

We have some CS people on E.SE; what would you call it when someone wants to optimize a two-second process to load data, though once loaded it will be chewed on by an inefficient algorithm for hours?

In a CS context, I'd simply call this "premature optimization". The reason that phrase works is because, in that context, I'd expect most people to be familiar with this famous quote by Donald E. Knuth, or at least to have heard it referenced:

"Programmers waste enormous amounts of time thinking about, or worrying about, the speed of noncritical parts of their programs, and these attempts at efficiency actually have a strong negative impact when debugging and maintenance are considered. We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil. Yet we should not pass up our opportunities in that critical 3%."

If I wanted a more colorful term, I might call it something like "painting racing stripes on a tricycle" or, if it's about accuracy instead of speed optimization, perhaps "putting a laser sight on a nerf gun". A somewhat common security idiom would be "putting a vault door on a garden shed" or "a steel padlock on a cardboard box", etc.; the possible variations are endless.