A: Do you still remember me? We met at Lucy’s birthday party last week. I was so wasted and made a fool of myself.
B1) How could I forget you?
B2) How could I have forgotten you?
Q: Are B1 and B2 both interchangeable? Do they both mean "I will always remember you for that"? Does (2) have something to do with the past since it uses "have forgotten"?
B1 refers to forgetting at any time. B2 refers to forgetting during the period since the party. In your context B1 would be more usual, but this is not readily predictable just by considering the verb tense.
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B1 refers to forgetting at any time.
B2 refers to forgetting during the period since the party.
In your context B1 would be more usual, but this is not readily predictable just by considering the verb tense.