Sissy Milestones

Try on panties for the first time
Buy your first pair panties (separated from above because I think many of us have tried on a family member's or girlfriend's panties first)
Buy your first dildo or anal toy, and/or try anal masturbation for the first time (could be separated into two milestones, e.g. using your fingers first)
Try on other lingerie items (stockings, bras, etc.)
Expand from panties and buy other lingerie items like bras and stockings (again if you wore a family member's or girlfriend's bra first)
Buy your first pair of heels
Wear panties in public under your male clothes
Replace all your men's underwear with panties and wear panties 24/7
Try on make up
Buy a chastity cage
Have someone else control your chastity lock (key-holder)
Buy breastforms
Buy a wig or grow long hair
Buy women's jewelry
Buy perfume
Buy women's regular clothing (e.g. socks, pants, blouses, etc.)
Be dressed as a sissy/en-femme in public
Have only women's clothing and be dressed 24/7
Use hormones
Watch sissy hypno/anal trainers
Have a sissygasm
Cum through anal only
Douche/enema before anal play
Taste your pre-cum
Cum on your own face/cum in your own mouth
Eat your own cum
Serve a Mistress/Master
Become collared
Go out in chastity and plugged under your normal clothes
Get a corset
Practice sucking cock using a lifelike dildo
Post a picture of you presenting as sissy on the Internet
Post a video of you masturbating/being fucked like a sissy on the Internet
Webcam as a sissy
Have a sissy gangbang
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Shave your:

Clitty
Shave your sissy-pussy
Legs
Entire body
Shave/grow a landing strip
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With a real cock while presenting as a sissy:

Give your first handjob
Give your first blowjob
Receive your first facial
Lose your sissy virginity
Bareback for the first time