Seras is a well known micro-celebrity on anitwitter, he has a tendency to sent weird things to people and so the phrase for when you get something weird from him "My day be so fine, then boom, Seras" was born
Seras: *sends video of guy fucking a toaster*
Everyone else: My day be so fine, then boom, Seras
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.