Said sarcastically or mockingly to someone who just finished telling a story about some problem or issue in their life that sucks but you don't really care about.
Goorgen: Dude, my girlfriend just dumped me, I got fired from my job, and now my mom won't let me play World of Warcraft anymore.
Chris: Awwww, Sad Trip Bro.
honestly dont care they just say this because you are feeling sad about this
Girl: Omg my crush has a gf
Guy: Thats really sad bro