I'm thinking of a person who is accepted as part of a social group despite being annoying, awkward, slow, or otherwise undesirable. As a trope, this person tends to fall victim to the whims of others in the group, often serving as a scapegoat, a punching bag, or a prop in an unfavorable comparison with someone else in the group.
I like punching bag but I'm wondering if there's something that more specifically references that this person is accepted for the fact that they make everyone else look good.