Harry: the couch in the Griffindoor common room
Ron: on the train when it is heading home from 4th year
Fred: At the Weasley's house during Christmas
George: On one of your date by the black lake
Draco: one your second date right after he dropped you off at your dorm
Neville: When you two were in the green house doing some extra work
Marauder era
James: On a date to Hogsmead, it was your 3rd date
Remus: During Christmas break in the Library, you both stayed at the school
Sirius: When you two got stuck in detention for something HE did, you just had some blame put on you