What you did was, you sneaked up behind someone and, with one hand over your mouth, held the other over the person's head and counted silently to yourself. If and when the person noticed, they had to cover their own mouth, whereupon you would shout "[Victim's name] has [whatever number you had managed to count to, or alternatively a completely made up number] boyfriends!"

There was a variation where you held two crooked fingers over your mouth, and your victim had to do the same, and woe betide them if they got it mixed up... Woe betide indeed.

Another way to make someone have a large amount of boyfriends/girlfriends would be as follows:
1: Put your hands together, palms facing you, fingertips touching.
2: Approach someone and ask them to "Open the gates". They will then have to pull your hands from the middle so they swing out like saloon doors.
3: Tell them to "Pick some flowers" and watch as they pick imaginary flowers.
4: Ask them how many flowers they have. If they say "One", keep asking until they say five or many more.
The number of flowers they have after you’ve stopped commanding them to pick more damn flowers corresponds to the number of boyfriends/girlfriends they have. Not a very good insult considering that the person making the joke is highly unlikely to have a boy/girlfriend of their own.

The number of partners you have of the opposite sex is linked directly to how gay you are. For instance, a boy with over twenty girlfriends is pretty damn gay - but if he had fifty girlfriends, his gayness would shoot through the roof. Similarly, a girl with two hundred boyfriends is such an impossibly up-front lesbian that she might as well have a velvet-tipping machine strapped to her jowels.

A woman with 225 boyfriends wearing her newest velvet-tipping machine.