Someone who keeps a secret from a friend until the last minute.
It is compared to someone who soaks a bandage in hot water and slowly takes it off avoiding pain
Bestie 1: Heyy soo...are you going to that party tonight?
Bestie 2: Hell yeah!
Bestie 1: (Thinking: OMG her boyfriend is bringing some slut to that party D:) Greeeeeeeeeaaaaaat, see you there!
Bestie 1: (Blurts out) YOUR BOYFRIEND IS CHEATING ON YOU!!!
Bestie 2: WTF you bandage soaker, why do you tell me that now?!?! Now I feel awkward D: