1. You take a dump on a lovers chest while or before titty fucking (if that partner is a female.) Generally for the cacaphile only or as a domination and humiliation tool in BDSM games. See also Brown Showers. The steamer part is that it is very probably steaming from the freshness (Moisture rising from it) not to do with "steamrolling" it. Then it would have been called a "Cleveland Steamroller". It is probably named after Cleveland (Lucky us Clevelanders) because of the brown stripe left behind resembling the brown stripe on the orange Cleveland Browns Football Helmet. If you squish it down and then you spooge on it for syrup it becomes a "Boston Pancake". Don't know the origin of Boston in refernce to that act.
2. Often used as a breakup technique for angry lovers to wait till the other is asleep and dumping on their chest and leaving them to wake in it the morning after. Point made. Sexual intercourse isn't necessary beforehand technically. It is only for extra points with your pals since you obviously are only pretending to be making up and having sex to achieve this goal and are tricking the other person to get even. Usually done without knowledge of the victim if the "pooper" wants to escape alive.
1) Laying a deuce upon your partners chest, then,
2) Sliding your buttcheeks up and down your partner's chest in a wake of your mud river, AND
3) making an authentic sound of a steam-whistle blowing.
Only once the steam-whistle has been sounded have you actually completed a realistic and true Cleveland Steamer.
"Oh yeah, did you do the steam-whistle sound and everything?"
"Hellzyeah. Woke the neighbors up and everything!"