a slowballer is an internet word spun off of cornball or goofball. the verb form is slowballing, typically used when someone is being slow in a convo.
jeff: whats weong with bro?
bob: dw bros a slowballer lol
jeff: yoo finally ur back, what happened?
bob: i was tryna explain something to my lil bro but he was slowballin so hard.
jeff: wsp?
bob: i slowballed a convo and now they think im retarded...
jeff: certified slowballer xd
bob: stfu