Why do people make fun of goths?
First, I was a punk in the early 1980's, so I have some understanding of openly declaring that one is free of being bound by unexamined, antiquated, and constricting social constructs. We self-select those that think like us. I found that these groups have strict rules as much as "normal" society.
Gross generalizations ahead.
People tend to make fun of or get angry with anyone that doesn't fit into their social group. We are risk avoiders. We judge others on how safe they appear, how smart, how affluent, how mentally stable they are, and if they fit into our opinion of proper society.
If you wear a sports jersey from an opposing team, you may be mocked. If you promote a political party that they don't like, you are an idiot who shouldn't vote.
In most of those cases, unless you somehow advertise it, we don't know your affiliations.
If you intentionally dress to look like a dangerous, undead, society-hater (or Society for Creative Anachronisms - SCA, Vampires, and to some degree Steampunk and COSPLAY, etc.) then you likely will generate distrust, fear, and anger.
They may mock you without any intention of getting to know you. This "unjust" judgment bonds group members together and confirms their belief that "normal" society is messed up and they are sheep.
Society may deem them to be overly dramatic, underemployed, ineffectual, unclean, and society-loathing. If you were Lord or Lady Death, you would have a castle, not be serving a double decaf mocha and pumpkin spice latte to someone running late for their marketing meeting. Expect some stink-face.
Society is not kind to outsiders. All societies have a dress code. As a Goth, if you show up to a Goth gathering in a plaid shirt and pleated khakis with a spray on tan, expect stink-face.
well, they ain't laughing now!