[Susie:] Take, for example, their response to a reader who's feeling nervous about using found objects (like her hairbrush) as sex toys:
Now back to the nitty-gritty of your question: The only criteria to judge an impromptu sex toy, is to make sure it's perfectly smooth, with no sharp edges or seams. Vaginally, it can be any shape you like, since your vag is a cul-de-sac. But if you ever want to use something for anal penetration, you need to make sure it has a flange (flared base). In that case, you hairbrush is fine for that, too.Next time one of my friends won't lend me something, I'm totally going to accuse them of masturbating with it.
If you want to use your "found dildo" more than once, just make sure it's washable, non-porous. If it would survive a spin in the dishwasher, it's a good candidate. Your hairbrush is probably hard plastic, which is ideal.
Where's all your apprehension coming from, after your fun? Honestly, how many times do people stomp into your bedroom and demand to use your hairbrush?
Aretha: Like never. Listen, Kate: If you don't want people to use your brush, JUST SAY NO. No one going to press you about it.
Susie: I can't imagine anyone putting you on the spot: "I bet you‘ve been masturbating with your comb and that's why you won't lend it to me!"