Three ways to do it:

  • The character gets deeply humiliated right away.
  • Events surrounding the character are such that you immediately go, “That’s why X is so broken.”
  • The character is so deeply charming that you get over it.

You can also mix the three.

You can’t write a dull character who’s mildly unpleasant and expect the reader to buy that someone who merely isn’t all that bad is actually good, let alone interesting.  “Nice guys” in fiction, as in romance, need not apply.