Here are some options depending on the context:
General examples:
* as straight as an arrow - classic and straightforward, implying perfect alignment and direction
* as straight as a line - emphasizing perfect linearity and lack of curves
* as straight as a ruler - suggests a precision and accuracy
* as straight as a die - implies fairness and honesty, often used for actions or decisions
* as straight as a poker - implies stiffness and lack of flexibility
More specific examples:
* as straight as a hair - emphasizing smooth and sleek appearance
* as straight as a path - implies clear and direct course of action
* as straight as a string - suggests tightness and resilience
* as straight as a spine - implies good posture and uprightness
Humorous examples:
* as straight as a drunkard's path - playful and ironic, implying a path that is not truly straight
* as straight as a banana - a funny and obvious exaggeration, highlighting the curved nature of a banana
To choose the best option, consider the specific object or situation you're comparing to "straight".