Ok, you guys know who I am, I know my stuff but I'm not so good at being sweet haha.

So basically I wear a t-shirt to the gym, I'm lean, 5.8inch bony wrist, 10/10 time it looks like it's my first day in the gym.

The gym I work out at is like the most sesat place ever. Basically you will see some super fat guys (85kg~95kg ish) who think they are damn "buff" but their max bench is 75kg  ... Then there's these guys who max bench like 110 Kg, at(or pass) genetic limit, been training for few years, but they ARE ALL on steroids (they talk openly bout it's use)  . Alot of people also wear lifting belts for 60~70kg squats in the smith machine.

So I often get approached and given dumb fuck advice. The gym owner (steroid user, 85kg, 13%~ bf) ask me to take mass gainers to have some "isi" before doing weights. I told him I'm on a surplus, and he's like if you eat food 80% will be fat gains, while if u bulk with mass gainers 80% will be muscle gains  . Everyone also thinks I'm mental for doing a full body program since "bro splits" are the way to go. But all this is fine, I just say ok smile and like do the "i will consider it" face and say "thank you bro for the advise"  .

The problem, sometimes there's these guys who will sibuk "correct" my form. Like for example, I use a thumb around grip while benching, and this guy actually interrupted me 2 times by coming and touching my hand to show me to use a suicide grip, it screwed my rest time and the set. Sometimes I'm bicep curling/incline pressing and a guy will go help me complete my last rep since I struggle abit, and this screws my progress tracking again  . There was also once this old uncle (he's abit muscular 20% bodyfat, so he thinks he's the shit) who came and start putting some lifting belt around my waist  while I was doing deadlifts (with 60kg only) saying I MUST ALWAYS wear it for safety.

I only can think of 3 solutions so far:
1. Lift with shirt off, no one will advise/interrupt me then cause it's clearly visible I'm trained and probably know my shit - But this is quite show off and sweat dirties the bench.
2. Wear a shirt with big bold red text, "I don't take Advise" - But this is very arrogant.
3. Tell them right in the eye "Please don't disturb me" - Firm but still quite aggressive.

I'm not good at this lar guys, so how do you like politely but firmly turn down people, and in a way they won't disturb you ever again?