It's pretty simple. You drive to wooded areas and **** strangers. You can do it in the car if it's a bit chilly, but if the weather permits you tend to do it up against trees or on the bonnet.
Would you like to attend with me one day? No pressure - you can stay in the car and masturbate if you don't feel comfortable.
Well nor would I. But we must assume that Kelvin and his glw are bang up for that sort of thing and - given your presence at this event - so are you.
I think Kelvin's presence would be the least of your worries, tbh. Looking up from the act and seeing Kelvin and chums knocking one out to your performance would at the very least put a chap off his stroke, you'd have thought.
I think it's afterwards that would be difficult. After all, in the heat of the moment these things are all very well, but in the clammy, reasty aftermath as one extracts oneself from this women and she reaches for the wet wipes, what does one do? Simply button up one's fly, nod at the assembled throng while studiously avoiding eye contact and scuttle back to one's vehicle?