[Mempho]

In a vacuum, pumping a hand in order to achieve the proper odds to draw from the turn to the river is absolutely ridiculous. Of course, you may still raise for other reasons (free card on the turn). The QJs hand is obviously a terrible example because, as pointed out, this has way too many effective outs to throw away even heads up in a small pot.

In order to illustrate, I think you should take 23s in the big blind against a sole limper that only plays broadway hands and pairs 77 and up. It the flop comes K Q J with two of your suit, the correct play is to check-fold. The only time your semibluff is likely to work is if he holds 77-99 and that is too unlikely. You can't beat him in a showdown unless you make your flush and, in this case, to cap the flop with him to give yourself odds to draw on the turn is absolutely ludicrous.

Now, there are times when capping the flop is a good idea (the QJs example can be capped for the sigma of value and FE) and that is why your roommate is many times making a +EV play but for a donkish reason.