Basic ones:

• the first time you do it
• the first time you get a bj/head
• the first time you made a woman cum

Unusual ones:

• the first time you do a threesome with a woman and a guy
• the first time you do a threesome with a woman and a woman
• the first time you do a group encounter
• the first time you do a gangbang with buddy's wife/GF
• the first time you do a gangbang with your wife/GF

Bizarre ones:

• the first time you are member of a porn video crew
• the first time you do it with a porn star (no cam)
• the first (& every) time you are in a polyamorous living arrangement

Heavy ones:

• the first time you do it with the woman you eventually marry
• the first time you do it during an extramarital affair
• the first time you do it after you know the marriage is over
• the first time you do it minus a testicle (hurts like fuck)

best regards,

buck