Does it ever bother you when someone has a snake for a pet and it's keep in a small tank?

Depends on the snake (and what you mean by 'small'). Some snakes (like corn snakes) are uncomfortable in too large of a space. They feel more secure in a smaller area.

It depends on what you would call 'small'.

In my opinion, the length should be at least half an inch shorter than the snake itself, and the height should be at least half the length of the snake with some room for bedding, toys, water and places to sleep/hide.

Only because I hate snakes. Give me the heebee geebee's.

bothers me when any animal is kept in a space that is too small for their happiness, but it depends on the kind of snake to know whether it likes small spaces or big spaces.