There's no shame in avoiding an opponent who's too good for you to beat. The only shame, really, is tangling with such a foe because either pride or boredom won't allow you to disengage. Boredom will cause you to play a higher limit than you're used to, just because it's the only game going at the moment. Boredom will get you stuck in a short-handed game, because there, the action's more frequently on you. Boredom will make you raise when you should fold, because you want to stay involved.
Boredom costs plenty.
Don't let it cost you. Treat your Internet poker exactly as you treat your live play. If you see a short-handed game with a couple of weak players whom your notes tell you that you can crush, by all means go after them. Go do something else. Find a different game on a different site, or just don't play.