When I run into a Smurf in a game they commonly do any number of these.
1) Troll pick a champ in a Role for FUn (Trust I have 1 million mastery with Ziggs its OP)
2) Often play VERY Drunk or Stoned to the point they are just inting. For FUn
3) Yell at team for not understanding the game like they do
4) Threaten to AFK if X does not happen (someone in champ select to get the role they want) becuase "Its my Smurf IDK"
5) Soft int (Ping Gank top, starts the gank and when their laner has Committed all-in, they run and let them die) lol for FUn
6) Try out new builds that Will not work (Garen Attack speed is going to be OP I know it, nope no Def items even boots cause I need to run fast) for FUn
7) Give up at the drop of a hat. (Zed FB 4m in GG FF@15) its a waste of time you noob! Im going to afk if you vote no.
There are so many others too all of which HURT the League Rank system.