Best friends sis

[Mperez3]

How do u tell ur best friend that his sister wants to give u a blowjob?

[FreeFall]

If you don't like her and want her to stop, you handle it yourself. Tell her you're not interest, don't like her like that, and she needs to quit it.
If you want your friend to deal with his sister, then you just say "hey your sister's making sexual advances towards me that I don't like or appreciate can you get her to stop that?"

But if everything's mutual between you two (you like each other) or are secretly dating, you don't say anything.

[West Coast Sheriff]

If you don't like her and want her to stop, you handle it yourself. Tell her you're not interest, don't like her like that, and she needs to quit it.
If you want your friend to deal with his sister, then you just say "hey your sister's making sexual advances towards me that I don't like or appreciate can you get her to stop that?"

But if everything's mutual between you two (you like each other) or are secretly dating, you don't say anything.
What she said

[DerBear]

Well. regardless if you do want it. I would suggest you decline anyway as something like this can seriously damage a friendship. I mean I bet if your best friend new his sister wanted to do that to you that he would not exactly be happy or supportive about it.

My advice decline the offer (I don't know from your post if you want it or not but decline it anyway) and just lead your life. If she does keep asking then you might want to mention something to an adult or your best friend but try to sound concerned. As something like this could cause the friendship to become damaged.