How are Watson and Holmes presented as different male characters?

At the beginning of The Sign of Four, it is clear that Sherlock Holmes intimidates John Watson. Although Watson is a doctor and a war veteran and quite accomplished in his own right, Holmes's confidence and intelligence make Watson reluctant to confront him about his drug abuse. Watson endures Holmes's egotism; he is fascinated by Holmes's powers of deduction and the adventures his work provides for both of them.
Holmes is not especially skilled in interacting with other people. He tends to be tactless, uninterested in others, and insensitive to others' feelings. He does not mean to give offense but frequently accomplishes just that. Watson, on the other hand, is attuned to the feelings of others and provides a buffer when Holmes is interacting with clients and suspects.
It is no surprise, then, that Watson should strike up a romance with Miss Morstan and end up engaged to her. When Watson announces the engagement to Holmes, he groans and tells Watson he cannot congratulate him because

love is an emotional thing, and whatever is emotional is opposed to that true cold reason which I place above all things. I should never marry myself, lest I bias my judgment.

Instead of taking offense, Watson is able to laugh and accept his friend and colleague's lack of social skill.