I Purple You
Created by Kim Taehyung of BTS, "I purple you" holds a deep and special meaning to the fandom. It is much more than "I love you" as purple is the last color of the rainbow and means "I will trust, love, and support you for a very long time."

IMPORTANT! "I purple you" loses its meaning and becomes "I hate you" when it's not said by ARMYs to BTS and the reverse. The reason behind it is that other artists/groups will feel like their fans are bringing up someone else in their interactions, immediately making them feel bad. Thus, it's good to avoid using it.
BTS: "We'll see each other again, ARMY! We purple you!"
ARMY: "We purple you, too!"

Fan: "I purple you!"
Not-BTS: "What does that mean... Ugh, come on, why would you use a BTS phrase? Just say you support and love me."