The most effective way that I've found is to push your boner to the side, if that makes sense. The problem with this is that you gotta hide the act of pushing your boner to the side.
What's a better way? Don't you dare say folding your arms...
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Why hide it? I prefer to just whip it out, point it at the nearest of age female and tell her to get busy, since its not gonna suck itself.