The phrase "私は大したマヌケだったな" (meaning "I was such a huge fool/idiot") contains the word マヌケ (manuke), which isn't considered strong profanity or inherently vulgar, but it can be mildly offensive or rude depending on context. Here's a breakdown:

1. マヌケ (manuke)
- Meaning: "Fool," "idiot," "blockhead," or someone who is clueless/inept.
- Strength: It's less harsh than words like バカ (baka) or アホ (aho) but still an insult. Think of it as "doofus" or "numbskull" in English — not a swear word, but derogatory.
- Context: When used self-deprecatingly (as in your example), it's often humorous or regretful, not aggressive. Directed at others, it can be rude.

2. Why might it be bleeped?
- Media Sensitivity: Some TV/radio shows censor even mild insults for audience appropriateness (e.g., daytime TV).
- Comedic Effect: Bleeping can exaggerate the self-criticism for humor.
- Cultural Nuance: While not profane, マヌケ implies incompetence, which might be softened with a bleep in conservative contexts.

3. Is it "strong language"?
- No, by Japanese standards. True profanity (e.g., くそ/kuso, ちくしょう/chikushō) is far stronger. マヌケ is closer to "jerk" or "moron" in English — potentially bleeped in kids' shows but not in most adult content.

Verdict:
- Not profane, but insulting/rude if aimed at others.
- A bleep here would likely be for comedic exaggeration or ultra-conservative censorship, not due to genuine vulgarity.

If you heard this bleeped in media, it was probably for tone/context, not because the word itself is inherently offensive. For reference, it's much milder than English swear words like "f**k" or "s**t."