Finneas Details Awkward Moment With Taylor Swift

Finneas and Taylor Swift don't have any 'Bad Blood' between them ... but, he says his blood still runs cold whenever he thinks about an awkward encounter they had!

The 10-time Grammy winner sat down for an interview with The Guardian, published Saturday ... and, he reflected on a mortifying moment between him and T-Swift when he attended her birthday party.

Finneas said Taylor thanked him for coming to her birthday party ... and, he responded, “Thank you for coming!” -- to her own party!

To be real ... we've all been there -- telling a server at a restaurant to enjoy their meal or an usher at a theater to also enjoy the show. It can get real darn awkward, but it seems Finneas is taking his blunder in stride.

BTW ... this was a joint interview with Finneas and Ashe -- a singer-songwriter he's collaborating with -- and, she's got her own dose of awkward to add.

Ashe says she ran up to Margot Robbie at a costume party and told her people said they looked alike ... total cringeworthy over-excited fan behavior Ashe hasn't lived down either.

Of course, Margot's well-known for being just as gregarious as Taylor ... and, Ashe confirms she played the whole situation off well.