3. Bc4 Sicilian

I've seen this line many times in my games. How to counter it

P.s. I am playing black

I switched recently from Caro-Kann to Sicilian, so I am lacking the experience.
I played couple of games and I tried your variant as black two or three times and I just don't like where it leads to. 
Instead, I switched to this variant and I decisively won all my games. And I liked my strong position very much too

Just we continue to play 3)...e6 4) Nc3 Nf6 5) d4 cxd4 6) Nxd4 or 3)...Nf6 4) Nc3 a6 5) d4 cxd4 6) Nxd4

Otherwise White can opt for timorous openings or at equal luck position ex. 1) e4 c5 2) Nf3 Nc6 3) d4 cxd4 4) Nxd4 Nf6 5) Nxc6 bxc6 Black player is happy in the sense he plays an opening that is potentially less dangerous, less disadvantageous etc. for himself not in the sense he is in a winning position, he cannot lose etc.

Ban that move please. Make it illegal. I write play d4 to my opponents in the chat lmao. Even if they play bc4 I try to convince them to play into Sozin line.

Well, just develop- ...Nc6, ...Nf6, ...e6 etc.

3.Bc4 is an OK move, but it does not create any serious threats, so you can develop normally.

It's not completely stupid. It totally negates the white bishop and you'll kick him out of the center completely by (b5), your white square bishop will move to b7 sniping white's weak center and the king, then knights go forward and are completely safe pressuring white's weak center even further. When I played c5-d6, white bishop would always harass my queen side knight and eventually double my pawns, which is not end of the world but I just don't like that kind of thing happening to me right in the opening

Just develop normally and if they try to fried liver you, play e6