Mariah Carey Explains Stealing Meryl Streep's Golden Globes Seat

Mariah Carey had a huge "oops" moment at the Golden Globes ... and no one was more understanding than Meryl Streep.

We got Mariah leaving Poppy in WeHo Sunday night and asked her about stealing Meryl's seat at one point during the show ... plopping down next to Steven Spielberg before realizing what she had just done.

Mariah felt terrible about it right after ... apologizing profusely. And it's obvious she still felt bad way after the show ended.