need advice on dealing with a creepy coworker

I have this one male coworker who is ALWAYS staring at my boobs. It’s not even subtle, he’s consistently doing it since the past few days. The seating arrangement is in such a way that normally his back is positioned in front of me, but he’ll consistently look back so many times and give me creepy stares.

I’m feeling so uncomfortable and objectified so I’m wearing a thin jacket over my top these days but it’s starting to get hot and it’s not a feasible long term solution😭 Also no idea how to report this or who to report it to because I technically have zero proof that he’s staring at my boobs. Idk if I should call him out directly but I feel like he’s going to start holding grudges against me and sabotage me later. Please help me out because I’m at my wits’ end.