0. Don't fight, you'll lose sooner or later (sooner) and it sets a bad example of solving problems later (you can get angry and punch someone in the face, but this won't help when dealing with bank manager). Defend yourself if attacked (grab anything hard within your reach and just smash it against the leader of the bullies, preferably his head) but do not go into the fight just because it's expected ("he called you a pussy, are you going to do something about it?") of you.
1. Give no reaction at all. No replies, witty comebacks and so on. The less you react to them the more dumb they look in front of others. Also were there is no victim, there can be no attacker.
2. For the next 30 days, EVERYDAY, meditate. Eyes opened slightly wider than normal, and look at ONE point only, ALL time. Start with 5 minutes first day and add 1 minute extra until you get to 20-30 minutes. While doing this imagine you're breathing air in your belly/guts. Breathe slow but deep. Focus your mind on the one point and breathing deep. Ignore other thoughts. I can routinely out-stare cops, bouncers, not to mention "non-muscle power" people. Just remember to...
3. ...smile while you're looking at them. Warm smile, not funny smile.
4. If you're afraid, whatever the cause, breathe deeply (multiple times) in and repeat in your mind "I accept my fear". Do it until the fear starts going away. Control your body with breathing and your mind with forcing it from "fear/reaction" to "what was that sentence I'm supposed to repeat?".
That is the quickest fix you can apply. Calm, confident look in eyes that can be held with anyone (meditation), smile (disarms negative energy), control of the fear (breathing and taking mental focus away from fear), give no reaction (not playing their game).
Long term solution - start weightlifting. Generally the bigger you are the less people mess with you.
No amount of money is gonna make you more confident in their presence, the best you can get for money is buying respect through expensive stuff, but it will make THEM less confident not YOU more confident.
When you are in control of a social environment
Will never happen, don't even propagate this attitude, it's extremely damaging, borderline on "psychological" HIV.
Also - you're a hypocrite and need to taste your own medicine - silly attempt at insult here gets you a quote:
People are generally disrespectful, two-faced, hypocritical
That is "you from a thread that comes to mind" talking about "yourself in this thread". Disrespectful, two faced hypocrite. No wonder others treat you like they do.