PVP and PVE highlights of various kinds.

Examples:

• Killsprees and multikills in pvp

• Rare medals in pve like Ghost or We Ran

• 1vMany situations like clutching a round of Trials

• Playing raids or strikes flawlessly

• Day1 raid race highlights such as boss clears and loot drops

• Exotic loot drops, especially post raid or in Trials flawless

• Rare triumphs or title unlocks/guilds

I'm sure there's other stuff, but that immediately springs to mind.