Imagine Person A and B of your OTP are really great friends who have had feelings for each other for a long time, but don't know how to confess them.
One day, A and B get into an argument over something small, and in order to to get B to be quiet, A roughly kisses him/her.
This then leads to both of them making out while A bends B over a surface, making love moments later. When A gets off of B, both of them confess their feelings.
A then asks B out, B saying that they would love to go out with A.