My cock is broken! Seriously, the internal shaft has a break in it so when I get hard it just points straight down vs standing up. (it's been like that most of my life) I think I broke it very early when I first started getting erections trying to see if it was bendable, but I digress. So it is not a problem for me and is easily concealable even when I'm fully hard. But looking at your Media pics Brianhalem, its does appear that your cock does point straight out when hard. (nice cock by the way) So this could be a problem for you.
So I too recommend what others have said. Try to jerk off beforehand until you have nothing left, then you'll be less likely to be able to get a serious erection. If you're a bottom like me I know how hard it is to control. The second I see another's man cock in the lockeroom (or elsewhere), I immediately begin to fantasize about how nice it would feel inside of me rubbing against my prostate, and before long I'm stiff as a board. But also as said, being in a non-sexual situation with friends and family might help to curtail that.
But if they don't know, I too would be terrified about my cock having a mind of its own and "outing me" at an inopportune time in front of close family. Sometimes, I just can't control it.