I shall begin with the good old "thank me later"
Translation- I have no actual insight to offer on this game, but if I win this bet people will think I know what I'm doing!
"Everyone and their MOM are on this team, so I'm taking the other side!"
or
"80% of the public are on this team, FADE THE PUBLIC!!"
Translation: I am too lazy or just flat unable to actually cap this game, but I am such a sharp contrarian!
"Unranked home favorites cover like 60% of the time vs ranked teams!"
Translation: I haven't actually done any research to back this up, but I've seen other people on the forum say it, so it must be true!!
"Team A's leading scorer is out!! OMG! Hammer this now before the line goes up!!"
Translation: I believe that I happened to check the injury report before the oddsmakers got a chance to check it. Therefore this injury is totally not factored into the line already!
"I have been on fire lately! So I figured I would start posting my picks on here to share the wealth!!"
Translation: When I inevitably start posting my usual losing picks, I can save face by saying that I was so hot that I was due for a cold streak
This next one is really not betting forum related, but if you browse some sports forums from time to time, you will see this insanely frequently: When a topic is about what their team needs to do to win the game, some doofus will always chime in with this: "Score more points than the other team!"
This joke was marginally clever the first 100,000 times it was said before 1990.
I'm sure I missed a few, feel free to add