On Topic:
Personally, I can not imagine experiencing this at all. Nor can I imagine even thinking of this prior to this thread. However, I can see how it would gross out some, be weird to those with "traditional" parent relationships, and anecdotal to those with more "evolved" parental interactions. To each their own.
Off Topic:
Personally, I find it interesting when those who find a title/topic so disconcerting, that they are compelled to read the thread and then make derogatory remarks. If the title suggests something that offends your sensibilities, why read it? If after reading your concern is confirmed, why spend time and energy castigating the OP and those not offended? There is a difference, for me, in disagreeing with an opinion (as I am doing) and suggesting that someone's interest crosses the line of sharing (not what I am doing). That decision is for the ToS and the Mods.
Additionally, I find it somewhat disingenuous to even want to subject someone's topic to a non-exsitent test of appropriateness on a website with a prime mission of discussing large penises. In fact, from large penis discussion to dad's cum rag, seems a more logical progression than, say, from large penises to recipes. All that being said, ultimately I am glad we all have the right to freedom of speech and expression within the set rules.
Apology:
Sorry for the hijack, just need to get these things out once in a while.
Return to Topic:
If Dad was concerned about being discovered, he would have taken more precautions. Seems he, and probably Mom, could care less (or were just careless), and/or simply did not expect the generous gesture. It'd be interesting to hear if Dad/Mom/they had a reaction to your discovery.
Hope you used the fabric softner...