Relive the memories.
If you're trying to create a mood conducive to flirtation, leave out the sob stories about how you got your ass kicked by a senior for flirting with his girl (but you got suspended! WTF?!) and focus on the good times.
Sneaking tall boys into homecoming games and downing them underneath the bleachers, consuming questionable juice concoctions at parties and dry humping in the woods, the way Mr. Stock used to drool out the side of his mouth as he talked about America—wasn't high school weird? Reminiscing about the positives will keep you from the reality of your boring adult life, where you wake up at the same time each morning, eat practically, and make reasonable decisions that won't negatively impact your job.
Remind each other of a time when—in hindsight—there was less drudgery. WE'RE NOT DEAD YET, HURRAH! Now go have sex.